Pattern forming method

ABSTRACT

A pattern forming method which uses a positive resist composition comprises: (A) a fluorine-free resin capable of increasing its solubility in an alkaline developer under action of an acid; (B) a compound capable of generating an acid upon irradiation with an actinic ray or radiation; (C) a fluorine-containing resin having at least one group selected from the group consisting of (X) an alkali-soluble group, (XI) a group capable of decomposing under action of an alkali developer and increasing solubility of the resin (C) in an alkaline developer and (XII) a group capable of decomposing under action of an acid and increasing solubility of the resin (C) in an alkaline developer; and (D) a solvent, the method comprising: (i) a step of applying the positive resist composition to a substrate to form a resist coating; (ii) a step of exposing the resist coating to light via an immersion liquid; (iii) a step of removing the immersion liquid remaining on the resist coating; (iv) a step of heating the resist coating; and (v) a step of developing the resist coating.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pattern forming method utilizing apositive resist composition usable in a lithography process formanufacturing semiconductors, such as ICs, and circuit boards for LCDsand thermal heads, and other photofabrication processes. Morespecifically, the invention is concerned with a pattern forming methodutilizing a positive resist composition suitable for exposure performedwith a projection exposure apparatus for immersion lithography using asa light source far ultraviolet rays with wavelengths of 300 nm or below.

2. Description of the Related Art

With the growing need for finer semiconductor devices, it has beenadvanced to adopt exposure light sources having shorter wavelengths andprojection lenses having higher numerical apertures (higher NAs). Up tonow, steppers using as light sources ArF excimer laser with a wavelengthof 193 nm and having NA of 0.84 have been developed. As generally wellknown, the resolution and the focal depth of these machines can be givenby the following expressions;

(Resolution)=k ₁·(λ/NA)

(Focal depth)=±k ₂ ·/NA ²

where λ is the wavelength of a exposure light source, NA is thenumerical aperture of a projection lens, and k₁ and k₂ are coefficientsconcerning a process.

Although steppers using as light sources F₂ excimer laser with awavelength of 157 nm are under study with an eye toward achieving higherresolution by further shortening of the wavelengths of exposure lightsources, it is very difficult to stabilize production costs andqualities of apparatus and materials since lens materials used inexposure apparatus and materials used for resist in order to ensureshorter wavelengths are confined within very narrow limits, and fearsare arising for completion of exposure apparatus and resist havingsufficient performance and stability within a required period.

As an art of heightening the resolution in an optical microscope, themethod of filling the space between a projection lens and a testspecimen with a liquid having a high refractive index (hereinafterreferred to as an immersion liquid), or the so-called immersion method,has hitherto been known.

This “immersion effect” can be explained as follows. In immersionlithography, the foregoing resolution and focal depth can be given bythe following expressions;

(Resolution)=k ₁·(λ₀ /n)/NA ₀

(Focal depth)=±k ₂·(λ₀ /n)/NA ₀ ²

where λ₀ is the wavelength of a exposure light source in the air, n isthe refractive index of an immersion liquid relative to the air and NA₀is equal to sin θwhen the convergent half angle of incident rays isrepresented by θ. That is to say, the effect of immersion is equivalentto the use of exposure light with a 1/n wavelength. In other words,application of the immersion method to a projection optical systemhaving the same NA value can multiply the focal depth by a factor of n.

This art is effective on all shapes of patterns, and besides, it can beused in combination with super-resolution techniques under study atpresent, such as a phase-shift method and an off-axis illuminationmethod.

Examples of apparatus utilizing this effect for transfer of fine circuitpatterns in semiconductor devices are disclosed in JP-A-57-153433 andJP-A-7-220990, but these documents have no description of resistsuitable for immersion lithography.

Recent progress of immersion lithography is reported in Proceedings ofInternational Society for Optical Engineering (Proc. SPIE), vol. 4688,p. 11 (2002), J. Vac. Sci. Technol. B, 17 (1999), Proceedings ofInternational Society for Optical Engineering (Proc. SPIE), vol. 3999,p. 2 (2000), and WO 2004/077158.

In order to supplement the sensitivity drop by light absorption from theresist for KrF excimer laser (248 nm) onward, the image forming methodreferred to as a chemical amplification method has been adopted as amethod of patterning resist. To illustrate an image forming methodutilizing chemical amplification by a positive-working case, images areformed in a process that exposure is performed to cause decomposition ofan acid generator in the exposed areas, thereby generating an acid, andconversion of alkali-insoluble groups (groups insoluble in an alkalinedeveloper) into an alkali-soluble groups (groups soluble in an alkalinedeveloper) by utilizing the acid generated as a reaction catalyst iscaused by bake after exposure (PEB: Post Exposure Bake) to enable theexposed areas to be removed by an alkaline developer.

In a general resist process used for formation of resist patterns, aresist composition is coated evenly on a substrate by use of a spin coatmethod, the substrate is heated in order to evaporate a resist solvent,the substrate is cooled to room temperature, the resist coating isexposed to light via a mask bearing the desired patterns, PEB is carriedout immediately after the exposure, the resist coating thus treated isimmersed in a developer after cooling to room temperature, the developeris rinsed out with water, and then the thus patterned resist coating isdried by a spin dry method.

Application of immersion lithography to chemical amplification resistaccording to the foregoing general resist process requires furtherimprovements in development defects appearing after development.

SUMMARY OF THE INVENTION

An object of the invention is to provide a patterning method which canensure formation of patterns improved in development defects appearingafter development in the case of performing immersion lithography.

Exemplary aspects of the invention are pattern forming methods describedbelow, and thereby the aforesaid object of the invention is attained.

(1) A pattern forming method which uses a positive resist compositioncomprising:

(A) a fluorine-free resin capable of increasing its solubility in analkaline developer under action of an acid;

(B) a compound capable of generating an acid upon irradiation with anactinic ray or radiation;

(C) a fluorine-containing resin having at least one group selected fromthe group consisting of (X) an alkali-soluble group, (XI) a groupcapable of decomposing under action of an alkali developer andincreasing solubility of the resin (C) in an alkaline developer and(XII) a group capable of decomposing under action of an acid andincreasing solubility of the resin (C) in an alkaline developer; and

(D) a solvent,

the method comprising:

(i) a step of applying the positive resist composition to a substrate toform a resist coating;

(ii) a step of exposing the resist coating to light via an immersionliquid;

(iii) a step of removing the immersion liquid remaining on the resistcoating;

(iv) a step of heating the resist coating; and

(v) a step of developing the resist coating.

(2) The pattern forming method as described in (1), wherein the resin(A) has a mononuclear or polynuclear alicyclic hydrocarbon structure.

(3) The pattern forming method as described in (1) or (2), wherein theresist coating is exposed to light of a wavelength of 193 nm.

(4) The pattern forming method as described in any of (1) to (3),further comprising a step of cleaning the resist coating surface priorto (ii) the step of exposing the resist coating to light via animmersion liquid.

(5) The pattern forming method as described in any of (1) to (4),wherein (iii) the step of removing the immersion liquid remaining on theresist coating is a step of removing the immersion liquid by feeding awater-miscible organic solvent onto the resist coating.

(6) The pattern forming method as described in (5), wherein thewater-miscible organic solvent is isopropyl alcohol.

In addition, the following are preferred embodiments of the invention.

(7) The pattern forming method as described in any of (1) to (6),wherein the resin (C) has a weight average molecular weight of 1,000 to100,000.

(8) The pattern forming method as described in any of (1) to (7),wherein the resin (C) is added in an amount of 0.1 to 5 mass % based onthe total solids in the positive resist composition.

(9) The pattern forming method as described in any of (1) to (4), (7)and (8), wherein (iii) the step of removing the immersion liquidremaining on the resist coating comprises forming a liquid film (puddle)of the immersion liquid and then removing the liquid film so as not toleft any liquid drops.

(10) The pattern forming method as described in (9), wherein the step ofremoving the liquid film is a step of removing the liquid film whilerotating the substrate at 500 rpm or above.

(11) The pattern forming method as described in any of (1) to (10),wherein the resin (A) comprises a repeating unit having a polycyclichydrocarbon group substituted by a hydroxyl group or a cyano group.

(12) The pattern forming method as described in any of (1) to (11),wherein the resin (C) is an alkali-soluble resin having thealkali-soluble group (X), and the alkali-soluble group (X) isrepresented by —C(CF₃)(CF₃)(OH).

(13) The pattern forming method as described in any of (1) to (12),

wherein the resin (A) comprises:

a repeating unit represented by formula (A1);

a repeating unit represented by formula (A2); and

a repeating unit represented by formula (A3),

wherein Xa, Xb and Xc each independently represents a hydrogen atom or amethyl group, R₁ represents a univalent organic group having a lactonestructure, R₂ represents a univalent organic group having a hydroxylgroup or a cyano group, and R₃ represents a univalent organic groupcapable of splitting off by the action of an acid.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described below in detail.

Additionally, the term “group (atomic group)” used in this specificationis intended to include both unsubstituted and substituted ones whenneither word substituted nor unsubstituted is added thereto. Forinstance, the term “alkyl group” is intended to include not only analkyl group having no substituent (an unsubstituted alkyl group) butalso an alkyl group having a substituent or substituents (a substitutedalkyl group).

[1] Fluorine-Free Resin (A) that can Increase Solubility in AlkaliDeveloper Under Reaction of Acid

One of resins used in a positive resist composition according to theinvention is a fluorine-free resin capable of increasing solubility inan alkaline developer under action of an acid.

Such a resin is preferably a fluorine-free resin having mononuclear orpolynuclear alicyclic hydrocarbon structures and capable of decomposingunder action of an acid to increase its solubility in an alkalinedeveloper (an acid-decomposable resin), and the resin is far preferablya resin having groups capable of decomposing under action of an acid toproduce alkali-soluble groups (hereinafter referred to as“acid-decomposable groups”) in either its main chain, or side chains, orboth (hereinafter referred to as “an alicyclic hydrocarbon-containingacid-decomposable resin”).

Examples of an alkali-soluble group include groups respectively having aphenolic hydroxyl group, a carboxylic acid group, a fluorinated alcoholgroup, a sulfonic acid group, a sulfonamido group, a sulfonylimidogroup, an (alkylsulfonyl)(alkylcarbonyl)methylene group, an(alkylsulfonyl)(alkylcarbonyl)imido group, a bis(alkylcarbonyl)methylenegroup, a bis(alkylcarbonyl)imido group, a bis(alkylsulfonyl)methylenegroup, a bis(alkylsulfonyl)imido group, a tris(alkylcarbonyl)methylenegroup and a tris(alkylsulfonyl)methylene group.

Of these alkali-soluble groups, a carboxylic acid group, a fluorinatedalcohol group (preferably a hexafluoroisopropanol group) and a sulfonicacid group is preferred over the others.

Groups suitable as groups capable of decomposing by an acid(acid-decomposable groups) are those obtained by substituting groupscapable of splitting off under action of an acid for hydrogen atoms ofthe alkali-soluble groups as recited above.

Examples of a group capable of splitting off under action of an acidinclude groups of formula —C(R₃₆)(R₃₇)(R₃₈), groups of formula—C(R₃₆)(R₃₇)(RO₃₉), and groups of formula —C(R₀₁)(R₀₂)(RO₃₉).

In those formulae, R₃₆ to R₃₉ each represent an alkyl group, acycloalkyl group, an aryl group, an aralkyl group or an alkenyl groupindependently. R₃₆ and R₃₇ may combine with each other to form a ring.R₀₁ and R₀₂ each represent a hydrogen atom, an alkyl group, a cycloalkylgroup, an aryl group, an aralkyl group or an alkenyl groupindependently.

Examples of a group suitable as an acid decomposable group include cumylester groups, enol ester groups, acetal ester groups and tertiary alkylester groups. Of these groups, tertiary alkyl ester groups are preferredover the others.

The alicyclic hydrocarbon-containing acid-decomposable resin ispreferably a resin having at least one kind of repeating units selectedfrom repeating units having partial structures containing alicyclichydrocarbon groups represented by the following formulae (pI) to (pV) orrepeating units represented by the following formula (II-AB).

In the formulae (pI) to (pV), R₁₁ represents a methyl group, an ethylgroup, an n-propyl group, an isopropyl group, an n-butyl group, anisobutyl group or a sec-butyl group, and Z represents atoms forming acycloalkyl group together with the carbon atom.

R₁₂ to R₁₆ each represent a straight-chain or branched alkyl group or acycloalkyl group independently, provided that at least one of R₁₂ toR₁₄, or either R₁₅ or R₁₆ represents a cycloalkyl group.

R₁₇ to R₂₁ each represent a hydrogen atom, a straight-chain or branchedalkyl group or a cycloalkyl group independently, provided that at leastone of R₁₇ to R₂₁ represents a cycloalkyl group. Further, either R₁₉ orR₂₁ is required to represent a straight-chain or branched alkyl group ora cycloalkyl group.

R₂₂ to R₂₄ each represent a hydrogen atom, a straight-chain or branchedalkyl group or a cycloalkyl group independently, provided that at leastone of R₂₂ to R₂₄ represents a cycloalkyl group. Alternatively, R₂₃ andR₂₄ may combine with each other to form a ring.

In the formula (II-AB), R₁₁′ and R₁₂′ each represent a hydrogen atom, acyano group, a halogen atom or an alkyl group independently.

Z′ represents atoms forming an alicyclic structure together with the twobonded carbon atoms (C—C).

The formula (II-AB) is preferably the following formula (II-AB1) orformula (II-AB2).

In the formulae (II-AB1) and (II-AB2), R₁₃′ to R₁₆′ each independentlyrepresent a hydrogen atom, a halogen atom, a cyano group, —COOH, —COOR₅,a group capable of decomposing under action of an acid,—C(═O)—X-A′-R₁₇′, an alkyl group or a cycloalkyl group. At least two ofR₁₃′ to R₁₆′ may combine with each other to form a ring.

R₅ represents an alkyl group, a cycloalkyl group or a group having alactone structure.

X represents an oxygen atom, a sulfur atom, —NH—, —NHSO₂— or —NHSO₂NH—.

A′ represents a single bond or a divalent linkage group.

R₁₇′ represents —COOH, —COOR₅, —CN, a hydroxyl group, an alkoxy group,—CO—NH—R₆, —CO—NH—SO₂—R₆ or a group having a lactone structure.

R₆ represents an alkyl group or a cycloalkyl group.

n represents 0 or 1.

The alkyl group which R₁₂ to R₂₅ each can represent in the formulae (pI)to (pV) is preferably a 1-4C straight-chain or branched alkyl group,with examples including a methyl group, an ethyl group, an n-propylgroup, an isopropyl group, an n-butyl group, an isobutyl group and asec-butyl group.

The cycloalkyl group which R₁₂ to R₂₅ each can represent or thecycloalkyl group which can be formed of Z and the carbon atom may bemonocyclic or polycyclic. Examples of such a cycloalkyl group includegroups each containing at least 5 carbon atoms and having a monocyclo,bicyclo, tricyclo or tetracyclo structure. The number of carbon atoms insuch a structure is preferably from 6 to 30, particularly preferablyfrom 7 to 25.

Suitable examples of such a cycloalkyl group include an adamantyl group,a noradamantyl group, a decaline residue, a tricyclodecanyl group, atetracyclododecanyl group, a norbornyl group, a cedrol group, acyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctylgroup, a cyclodecanyl group and a cyclododecanyl group. Of these groups,an adamantyl group, a norbornyl group, a cyclohexyl group, a cyclopentylgroup, a tetradecanyl group and a tricyclodecanyl group are preferredover the others.

Each of these alkyl groups and cycloalkyl groups may further have asubstituent. Examples of such a substituent include an alkyl group(1-4C), a halogen atom, a hydroxyl group, an alkoxy group (1-4C), acarboxyl group and an alkoxycarbonyl group (2-6C). Herein, the alkyl,alkoxy and alkoxycarbonyl groups each may further have a substituent,such as a hydroxyl group, a halogen atom or an alkoxy group.

The structures represented by the formulae (pI) to (pV) in the resinscan be used for protection of alkali-soluble groups. Examples ofalkali-soluble groups which can be protected by such structures includevarious groups which are known in this technical field.

More specifically, such a protected alkali-soluble group has a structureformed by substituting the structure represented by any of the formulae(pI) to (pV) for the hydrogen atom of carboxylic acid, sulfonic acid,phenol or thiol. Suitable examples of such a structure includestructures formed by substituting the structures represented by formulae(pI) to (pV) for the hydrogen atoms of carboxylic acid groups orsulfonic acid groups.

As repeating units having alkali-soluble groups protected by thestructures of formulae (pI) to (pV), repeating units represented by thefollowing formula (pA) are preferred.

In the formula (pA), each R represents a hydrogen atom, a halogen atomor a 1-4C straight-chain or branched alkyl group. A plurality of Rs maybe the same or different.

A represents a single bond, an alkylene group, an ether group, athioether, group, a carbonyl group, an ester group, an amido group, asulfonamido group, a urethane group, a urea group, or a combination oftwo or more of the groups recited above, preferably a single bond.

Rp₁ represents any of the formulae (pI) to (pV).

The most suitable of repeating units represented by the formula (pA) isa repeating unit derived from 2-alkyl-2-adamantyl (meth)acrylate ordialkyl(1-adamantyl)methyl(meth)acrylate.

Examples of a repeating unit represented by the formula (pA) areillustrated below, but these examples should not construed as limitingthe scope of the invention.

(In the following formulae, R_(x) is H, CH₃, CF₃ or CH₂OH, and Rxa andRxb are each a 1-4C alkyl group.)

Examples of a halogen atom which R₁₁′ and R₁₂′ each can represent in theformula (II-AB) include a chlorine atom, a bromine atom, a fluorine atomand an iodine atom.

Examples of an alkyl group which R₁₁′ and R₁₂′ each can representinclude 1-10C straight-chain or branched alkyl groups.

The atoms Z′ for forming an alicyclic structure are atoms forming arepeating unit having an alicyclic hydrocarbon structure which may havea substituent, particularly preferably atoms forming a repeating unithaving a bridged alicyclic hydrocarbon structure.

Examples of a skeleton of the alicyclic hydrocarbon formed include thesame ones as alicyclic hydrocarbon groups which R₁₂ to R₂₅ can representin the formulae (pI) to (pV).

The skeleton of the alicyclic hydrocarbon structure may have asubstituent. Examples of such a substituent include R₁₃′ to R₁₆′ in theformulae (II-AB1) and (II-AB2).

In the alicyclic hydrocarbon-containing acid-decomposable resin for usein the invention, groups capable of decomposing under action of an acidcan be incorporated in at least one type of repeating units chosen fromrepeating units having partial structures containing aliphatichydrocarbons represented by the formulae (pI) to (pV), repeating unitsrepresented by the formula (II-AB) or repeating units ofcopolymerization components described hereinafter.

Various kinds of substituents as R₁₃′ to R₁₆′ in the formula (II-AB1) or(II-AB2) may also become substituents of atoms Z forming an alicyclichydrocarbon structure or a bridged alicyclic hydrocarbon structure inthe formula (II-AB).

Examples of repeating units represented by the formulae (II-AB1) and(II-AB2) are illustrated below, but these examples should not beconstrued as limiting the scope of the invention.

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention preferably has repeating units each containing a grouphaving a lactone structure. As the group having a lactone structure, anygroup can be used as far as it has a lactone structure. Suitableexamples of a group having a lactone structure include groups having 5-to 7-membered ring lactone structures, preferably those which fuse withother ring structures to form bicyclo or spiro structures. Of the groupshaving lactone structures, the groups having lactone structuresrepresented by the following formulae (LC1-1) to (LC1-16) are preferredover the others. Alternatively, the groups having lactone structures maybe bonded directly to the main chain. The lactone structures used toadvantage are (LC1-1), (LC1-4), (LC1-5), (LC1-6), (LC1-13) and (LC1-14),and the use of specified lactone structures contributes to improvementsin line edge roughness and development defects.

Each lactone structure moiety may have a substituent (Rb₂) or needn't.Suitable examples of a substituent (Rb₂) include 1-8C alkyl groups, 3-7Ccycloalkyl groups, 1-8C alkoxy groups, 1-8C alkoxycarbonyl groups, acarboxyl group, halogen atoms, a hydroxyl group, a cyano group andacid-decomposable groups. n₂ represents an integer of 0 to 4. When n₂ is2 or above, a plurality of Rb₂s may be the same or different, or theymay combine with each other to form a ring.

Examples of a repeating unit containing a group having a lactonestructure represented by any of the formulae (LC1-1) to (LC1-16) includethe repeating units represented by the formula (II-AB1) or (II-AB2)wherein at least one of R₁₃′ to R₁₆′ is a group having the lactonestructure represented by any of the formulae (LC1-1) to (LC1-16) (forinstance, R₅ in —COOR₅ represents a group having the lactone structurerepresented by any of the formulae (LC1-1) to (LC1-16)), and repeatingunits represented by the following formula (AI).

In the formula (AI), Rb₀ represents a hydrogen atom, a halogen atom or a1-4C alkyl group. Examples of a suitable substituent the alkyl grouprepresented by Rb₀ may have include a hydroxyl group and halogen atoms.

Examples of a halogen atom represented by Rb₀ include a fluorine atom, achlorine atom, a bromine atom and an iodine atom.

Rb₀ is preferably a hydrogen atom or a methyl group.

Ab represents a single bond, an alkylene group, a divalent linkage grouphaving a mononuclear or polynuclear alicyclic hydrocarbon structure, anether group, an ester group, a carbonyl group, or a divalent groupformed by combining two or more of the groups recited above.

Ab is preferably a single bond or a linkage group represented by-Ab₁-CO₂—. Ab₁ is a straight-chain or branched alkylene group or amonocyclic or polycyclic cycloalkylene group, preferably a methylenegroup, an ethylene group, a cyclohexylene group, an adamantylene groupor a norbornylene group.

V represents a group having a lactone structure represented by any ofthe formulae (LC1-1) to (LC1-16).

A repeating unit having a lactone structure generally has opticalisomers, and any of the optical isomers may be used. Further, oneoptical isomer may be used by itself, or two or more of optical isomersmay be used as a mixture. When one optical isomer is mainly used, theoptical purity (ee) thereof is preferably 90 or above, far preferably 95or above.

Examples of a repeating unit containing a group having a lactonestructure are illustrated below, but these examples should not beconstrued as limiting the scope of the invention.

(In each of the following formulae, R_(x) is H, CH₃, CH₂OH or CF₃)

(In each of the following formulae, R_(x) is H, CH₃, CH₂OH or CF₃)

(In each of the following formulae, R_(x) is H, CH₃, CH₂OH or CF₃)

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention preferably has repeating units containing groups havingalicyclic hydrocarbon structures (preferably polycyclic hydrocarbonstructure) substituted with polar groups. By introduction of suchrepeating units in the resin, adhesiveness to a substrate and affinityfor a developer can be enhanced. Examples of an alicyclic hydrocarbonstructure preferred in the alicyclic hydrocarbon structure substitutedwith a polar group include an adamantyl group, a diamantyl group and anorbornyl group, and examples of a polar group preferred in such astructure are a hydroxyl group and a cyano group. As groups havingalicyclic hydrocarbon structures substituted with polar groups, thoserepresented by the following formulae (VIIa) to (VIId) are suitable.

In the formulae (VIIa) to (VIIc), R_(2C) to R_(4C) each represent ahydrogen atom, a hydroxyl group or a cyano group independently, providedthat at least one of them represents a hydroxyl group or a cyan group.The case where one of R_(2C) to R_(4C) is a hydroxyl group and theremainder are hydrogen atoms and the case where two of R_(2C) to R_(4C)are hydroxyl groups and the remainder is a hydrogen atom are preferable.In the formula (VIIa), it is far preferred that two of R_(2C) to R_(4C)are hydroxyl groups and the remainder is a hydrogen atom.

Examples of repeating units containing groups represented by theformulae (VIIa) to (VIId) include the repeating units represented by theformula (II-AB1) or (II-AB2) wherein at least one of R₁₃′ to R₁₆′ is agroup represented by any of the formulae (VIIa) to (VIId) (for instance,R₅ in —COOR₅ represents a group represented by any of the formulae(VIIa) to (VIId)), and repeating units represented by the followingformulae (AIIa) to (AIId).

In the formula (AIIa) to (AIId), R_(1C) represents a hydrogen atom, amethyl group, a trifluoromethyl group or a hydroxymethyl group.

Examples of repeating units represented by the formulae (AIIa) to (AIId)are illustrated below, but these examples should not be construed aslimiting the scope of the invention.

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention may have repeating units represented by the followingformula (VIII).

In the formula (VIII), Z₂ represents —O— or —N(R₄₁)—. R₄₁ represents ahydrogen atom, a hydroxyl group, an alkyl group or —OSO₂—R₄₂. R₄₂represent an alkyl group, a cycloalkyl group or a camphor residue. Thealkyl groups of R₄₁ and R₄₂ may be substituted with halogen atoms(preferably fluorine atoms).

Examples of a repeating unit represented by the formula (VIII) areillustrated below, but these examples should not be construed aslimiting the scope of the invention.

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention preferably has repeating units containing alkali-solublegroups, far preferably repeating units containing carboxyl groups. Bycontaining such groups in the repeating units, resolution in contacthole uses is enhanced. Suitable examples of repeating units containingcarboxyl groups include repeating units containing carboxyl groups in astate that they are bonded directly to the resin's main chain, such asrepeating units derived from acrylic acid and methacrylic acid,repeating units containing carboxyl groups in a state that they areattached to the resin's main chain via linkage groups, and polymer chainterminals wherein alkali-soluble groups are introduced by using apolymerization initiator or chain transfer agent having analkali-soluble group at the time of polymerization. Therein, the linkagegroups may have mononuclear or polynuclear cyclic hydrocarbonstructures. However, repeating units derived from acrylic acid andmethacrylic acid in particular are preferred.

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention may further contain repeating units having alicyclichydrocarbon structures and not showing acid decomposability. Byintroduction of such repeating units, elution of low molecularcomponents from a resist coating into an immersion liquid at the time ofperformance of immersion lithography can be reduced. Examples of suchrepeating units include those derived from 1-adamantyl (meth)acrylate,tricyclodecanyl (meth)acrylate and cyclohexayl(meth)acrylate.

In addition to the repeating structural units recited above, thealicyclic hydrocarbon-containing acid-decomposable resin for use in theinvention can contain a wide variety of repeating structural units forthe purpose of controlling resistance to dry etching, suitability forstandard developers, adhesiveness to substrates, resist profile, andbesides, characteristics generally required for resist, such asresolution, thermal resistance and sensitivity.

Examples of such repeating structural units include repeating structuralunits corresponding to the monomers as recited below, but these examplesshould not be construed as limiting the scope of the invention.

By containing those repeating units, it becomes possible to make fineadjustments to properties required for the alicyclichydrocarbon-containing acid-decomposable resin, especially to:

(1) solubility in coating solvents,(2) film formability (glass transition temperature),(3) alkali developability,(4) thinning of film (hydrophilic-hydrophobic balance, alkali-solublegroup selection),(5) adhesion of unexposed areas to a substrate, and(6) dry etching resistance.

Examples of monomers suitable for the foregoing purposes includecompounds which each have one addition-polymerizable unsaturated bondand are selected from acrylic acid esters, methacrylic acid esters,acrylamides, methacrylamides, allyl compounds, vinyl ethers, or vinylesters.

In addition to those monomers, any other monomers may be copolymerizedso long as they are addition-polymerizable unsaturated compounds capableof forming copolymers together with monomers corresponding to thevarious repeating structural units mentioned above.

The molar content of each repeating structural unit in the alicyclichydrocarbon-containing acid-decomposable resin can be chosenappropriately for adjusting dry etching resistance, standard developersuitability, adhesion to substrates, resist profile, and characteristicsgenerally required for resist, such as resolution, thermal resistanceand sensitivity.

Examples of a preferred state of the alicyclic hydrocarbon-containingacid-decomposable resin for use in the invention include the following.

(1) A state of containing repeating units each having a partialstructure containing an alicyclic hydrocarbon represented by any of theformulae (pI) to (pV) (side-chain type).

The repeating units contained therein are preferably (meth)acrylaterepeating units each having a structure containing any of (pI) to (pV).

(2) A state of containing repeating units represented by the formula(II-AB) (main-chain type). However, the state (2) further includes thefollowing.

(3) A state of having repeating units represented by the formula (II-Ab)and maleic anhydride derivative and (meth)acrylate structures (hybridtype).

The content of repeating units having acid-decomposable groups in thealicyclic hydrocarbon-containing acid-decomposable resin is preferably10 to 60 mole %, far preferably 20 to 50 mole %, further preferably 25to 40 mole %, of the total repeating structural units.

The content of repeating units having partial structures containingalicyclic hydrocarbons represented by the formulae (pI) to (pV) in thealicyclic hydrocarbon-containing acid-decomposable resin is preferably20 to 70 mole %, far preferably 20 to 50 mole %, further preferably 25to 40 mole %, of the total repeating structural units.

The content of repeating units represented by the formula (II-AB) in thealicyclic hydrocarbon-containing acid-decomposable resin is preferably10 to 60 mole %, far preferably 15 to 55 mole %, further preferably 20to 50 mole %, of the total repeating structural units.

In the resin, the content of repeating structural units based on themonomers as further copolymerizing components can also be chosenappropriately according to the intended resist performance. In general,the proportion of such repeating structural units is preferably 99 mole% or below, far preferably 90 mole % or below, further preferably 80mole % or below, based on the total mole number of the repeatingstructural units having partial structures containing alicyclichydrocarbons represented by the formulae (pI) to (pV) and the repeatingunits represented by the formula (II-AB).

When the composition according to the invention is designed for ArFexposure use, it is appropriate to adopt resins not having aromaticgroups in point of transparency to ArF light.

As to the alicyclic hydrocarbon-containing acid-decomposable resin foruse in the invention, all of its repeating units are preferablyconstituted of (meth)acrylate repeating units. Herein, all the repeatingunits may be either acrylate repeating units alone, or methacrylaterepeating units alone, or a mixture of acrylate and methacrylaterepeating units. However, it is preferable that the acrylate repeatingunits is at most 50 mole % of the total repeating units. The alicyclichydrocarbon-containing acid-decomposable resin is far preferably aternary copolymer containing 20 to 50 mole % of repeating units havingpartial structures containing alicyclic hydrocarbons represented by anyof the formulae (pI) to (pV), 20 to 50 mole % of repeating unitscontaining lactone structures and 5 to 30 mole % of repeating unitshaving alicyclic hydrocarbon structures substituted with polar groups,or a quaternary copolymer further containing 0 to 20 mole % of otherrepeating units.

The resin preferred in particular is a ternary copolymer containing 20to 50 mole % of repeating units having acid-decomposable groups, whichare represented by any of the following formulae (ARA-1) to (ARA-5), 20to 50 mole % of repeating units having lactone groups, which arerepresented by any of the following formulae (ARL-1) to (ARL-6), and 5to 30 mole % of repeating units having alicyclic hydrocarbon structuressubstituted with polar groups, which are represented by any of thefollowing formulae (ARH-1) to (ARH-3), or a quaternary copolymer furthercontaining 5 to 20 mole % of repeating units having carboxyl groups, orrepeating units having alicyclic hydrocarbon structures but not showingacid decomposability.

In the above concrete examples each, Rxy₁ represents a hydrogen atom ora methyl group.

Rxa₁ and Rxb₁ each represent a methyl group or an ethyl groupindependently.

The alicyclic hydrocarbon-containing acid-decomposable resin preferablyhas repeating units represented by the following formula (A1), repeatingunits represented by the following formula (A2) and repeating unitsrepresented by the following formula (A3).

In the formulae (A1) to (A3), Xa, Xb and Xc each represent a hydrogenatom or a methyl group independently.

R₁ represents a univalent organic group having a lactone structure.

R₂ represents a univalent organic group having a hydroxyl group or acyano group.

R₃ represents a group capable of splitting off under action of an acid.

The repeating units represented by the formula (A1) are preferably therepeating units represented by the formula (AI) illustratedhereinbefore.

The proportion of the repeating units represented by the formula (A1) ispreferably 25 to 50 mole % of the total repeating units in the alicyclichydrocarbon-containing acid-decomposable resin.

The repeating units represented by the formula (A2) are preferably therepeating units represented by the formula (AIIa) or (AIIb) illustratedhereinbefore.

The proportion of the repeating units represented by the formula (A2) ispreferably 5 to 30 mole % of the total repeating units in the alicyclichydrocarbon-containing acid-decomposable resin.

The repeating units represented by the formula (A3) are preferably therepeating units represented by the formula (pA) illustratedhereinbefore.

The proportion of the repeating units represented by the formula (A3) ispreferably 25 to 50 mole % of the total repeating units in the alicyclichydrocarbon-containing acid-decomposable resin.

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention can be synthesized according to general methods (e.g.,radical polymerization). As examples of a general synthesis method,there are known a batch polymerization method in which polymerization iscarried out by dissolving monomer species and an initiator in a solventand heating, and a drop polymerization method in which a solutioncontaining monomer species and an initiator is added dropwise to aheated solvent over 1 to 10 hours. However, it is preferable to use thedrop polymerization method. Examples of a reaction solvent usable hereininclude ethers, such as tetrahydrofuran, 1,4-dioxane and diisopropylether; ketones, such as methyl ethyl ketone and methyl isobutyl ketone;ester solvents, such as ethyl acetate; amide solvents, such asdimethylformamide and dimethylacetamide; and solvents described later inwhich the present composition can be dissolved, such as propylene glycolmonomethyl ether acetate, propylene glycol monomethyl ether andcyclohexanone. It is preferable to perform polymerization by use of thesame solvent as used in the present resist composition. By doing so,development of particles during storage can be retarded.

The polymerization reaction is preferably carried out in an atmosphereof inert gas, such as nitrogen or argon. And the polymerization isinitiated using a commercially available radical initiator (e.g., anazo-type initiator or peroxide) as polymerization initiator. As theradical initiator, an azo-type initiator is suitable, and an azo-typeinitiator having an ester group, a cyano group or a carboxyl group ispreferable. Examples of such a preferable azo-type initiator includeazobisisobutyronitrile, azobisdimethylvaleronitrile and dimethyl2,2′-azobis(2-methylpropionate). Such an initiator may be addedadditionally in the course of polymerization, or may be added in severalportions, if desired. After the conclusion of the reaction, the reactionsolution is poured into a solvent, and the intended polymer is collectedas a powder or a solid. The concentration of a reaction system is from 5to 50 mass %, preferably from 10 to 30 mass %, and the reactiontemperature is generally from 10° C. to 150° C., preferably from 30° C.to 120° C., far preferably from 60° C. to 100° C.

When the composition according to the invention is used for theupper-layer resist of a multilayer resist, it is preferable that theresin of Component (A) contains silicon atoms.

As a resin containing silicon atoms and capable of decomposing underaction of an acid to increase the solubility in an alkaline developer, aresin containing silicon atoms in at least either its main chain or sidechains can be used. An example of a resin containing siloxane structuresin its side chains is a copolymer of an olefin monomer having siliconatoms in side chains, maleic anhydride and a (meth)acrylic acid monomercontaining an acid-decomposable group as its side chain.

The resin having silicon atoms is preferably a resin havingtrialkylsilyl structures or mono- or polynuclear cyclosiloxanestructures, far preferably a resin containing repeating units havingstructures represented by any of the following formulae (SS-1) to(SS-4), further preferably a resin containing (meth)acrylate, vinyl orallyl repeating units having structures represented by any of theformulae (SS-1) to (SS-4).

In the formulae (SS-1) to (SS-4), each Rs represents a 1-5C alkylgroups, preferably a methyl group or an ethyl group.

The resin having silicon atoms is preferably a resin containing at leasttwo different types of repeating units having silicon atoms, farpreferably a resin containing both (Sa) repeating units each having 1 to4 silicon atoms and (Sb) repeating units each having 5 to 10 carbonatoms, further preferably a resin containing at least one type ofrepeating units chosen from those having structures represented by theformulae (SS-1) to (SS-3) and repeating units having structuresrepresented by the formula (SS-4).

As to the resin of Component (A), the weight average molecular weightthereof is preferably from 1,500 to 100,000, far preferably from 2,000to 70,000, particularly preferably from 3,000 to 50,000. The dispersiondegree thereof is preferably from 1.0 to 3.0, far preferably from 1.0 to2.5, further preferably from 1.0 to 2.0.

The addition amount of resin of Component (A) is from 50 to 99.7 masspreferably from 70 to 99.5 mass %, of the total solids in the positiveresist composition.

[2] Compound (B) that can Generate Acid Upon Irradiation with ActinicRay or Radiation

The positive resist composition according to the invention contains acompound capable of generating an acid upon irradiation with an actinicray or radiation (which is also referred to as “an acid generator”).

The compound usable as such an acid generator can be selectedappropriately from photo-initiators for cationic photopolymerization,photo-initiators for radical photopolymerization, photodecoloring agentsfor dyes, photodiscoloring agents, compounds used in microresist andknown to generate acids upon irradiation with an actinic ray orradiation, or mixtures of two or more thereof.

Examples of such compounds include diazonium salts, phosphonium salts,sulfonium salts, iodonium salts, imide sulfonates, oxime sulfonates,diazodisulfone, disulfone and o-nitrobenzylsulfonate.

In addition, polymeric compounds having those groups or compoundscapable of generating acids upon irradiation with an actinic ray orradiation in a state of being introduced in their main or side chainscan also be used. Examples of such polymeric compounds include thecompounds as disclosed in U.S. Pat. No. 3,849,137, German Patent No.3914407, JP-A-63-26653, JP-A-55-164824, JP-A-62-69263, JP-A-63-146038,JP-A-63-163452, JP-A-62-153853 and JP-A-63-146029.

Further, the compounds capable of generating acids by the action oflight as disclosed in U.S. Pat. No. 3,779,778 and European Patent No.126,712 can also be used.

Of the compounds capable of decomposing upon irradiation with an actinicray or radiation to generate acids; compounds represented by thefollowing formulae (ZI), (ZII) and (ZIII) respectively are preferred.

In the formula (ZI), R₂₀₁, R₂₀₂ and R₂₀₃ each represent an organic groupindependently.

X⁻ represents a non-nucleophilic anion, preferably a sulfonic acidanion, a carboxylic acid anion, a bis(alkylsulfonyl)amide anion, atris(alkylsulfonyl)methide anion, BF₄ ⁻, PF₆ ⁻ or SbF₆ ⁻, far preferablyan organic anion having at least one carbon atom.

Suitable examples of an organic anion include organic anions representedby the following formulae.

In the above formulae, Rc₁ represents an organic group.

Examples of an organic group as Rc₁ include those containing 1 to 30carbon atoms, preferably alkyl groups, aryl groups and groups formed byconnecting two or more of those groups via one or more of linkagegroups, such as a single bond, —O—, —CO₂—, —S—, —SO₃— and —SO₂N(Rd₁)—.Rd₁ represents a hydrogen atom or an alkyl group.

Rc₃, Rc₄ and Rc₅ each represents an organic group. Examples of such anorganic group include the same organic groups as recited as thosepreferred by Rc₁, particularly preferably 1-4C perfluoroalkyl groups.

Rc₃ and Rc₄ may combine with each other to form a ring. The group formedby combining Rc₃ with Rc₄ is an alkylene group or an arylene group,preferably a 2-4C perfluoroalkylene group.

The organic groups particularly preferred as Rc₁ and Rc₃ to Rc₅ arealkyl groups substituted with fluorine atoms or fluoroalkyl groups attheir respective 1-positions and phenyl groups substituted with fluorineatoms or fluoroalkyl groups. When a fluorine atom or a fluoroalkyl groupis present, the acid generated by irradiation with light can have highacidity to result in enhancement of the sensitivity. On the other hand,when Rc3 and Rc4 combine with each other to form a ring, the acidgenerated by irradiation with light can also increase its acidity toresult in enhancement of the sensitivity.

The number of carbon atoms in the organic group of R₂₀₁, R₂₀₂ and R₂₀₃each is generally from 1 to 30, preferably from 1 to 20.

Two of R₂₀₁ to R₂₀₃ may combine with each other to form a ringstructure, and the ring formed may contain an oxygen atom, a sulfuratom, an ester linkage, an amide linkage or a carbonyl group. Examplesof a group formed by combining two of R₂₀₁, R₂₀₂ and R₂₀₃ includealkylene groups (such as a butylene group and a pentylene group).

Examples of organic groups as R₂₀₁, R₂₀₂ and R₂₀₃ include correspondinggroups in compounds (Z1-1), (Z1-2) and (Z1-3) described below.

The acid generator may be a compound having two or more of structuresrepresented by formula (ZI). For instance, it may be a compound having astructure that at least one of R₂₀₁, R₂₀₂ and R₂₀₃ in one compoundrepresented by formula (ZI) is bound to at least one of R₂₀₁, R₂₀₂ andR₂₀₃ in another compound represented by formula (ZI).

Examples of a further preferred component (ZI) include compounds (ZI-1),(ZI-2) and (ZI-3).

The compound (Z1-1) is an arylsulfonium compound represented by theformula (ZI) in which at least one of R₂₀₁ to R₂₀₃ is an aryl group,namely a compound having an arylsulfonium as its cation.

In such an arylsulfonium compound, all of R₂₀₁ to R₂₀₃ may be arylgroups, or one or two of R₂₀₁ to R₂₀₃ may be aryl groups and theremainder may be an alkyl group or a cycloalkyl group.

Examples of such an arylsulfonium compound include a triarylsulfoniumcompound, a diarylalkylsulfonium compound, an aryldialkylsulfoniumcompound, a diarylcycloalkylsulfonium and an aryldicycloalkylsulfoniumcompound.

The aryl group in the arylsulfonium compound is preferably an aryl groupsuch as a phenyl group or a naphthyl group, or a heteroaryl group suchas an indole residue or a pyrrole residue, far preferably a phenyl groupor an indole residue. When the arylsulfonium compound has two or morearyl groups, the two or more aryl groups may be the same or different.

One or two alkyl groups which the arylsulfonium compound has as requiredare preferably 1-15C straight-chain or branched alkyl groups, withexamples including a methyl group, an ethyl group, a propyl group, ann-butyl group, a sec-butyl group and a t-butyl group.

One or two cycloalkyl groups which the arylsulfonium compound has asrequired are preferably 3-15C cycloalkyl groups, with examples includinga cyclopropyl group, a cyclobutyl group and a cyclohexyl group.

The aryl group, the alkyl group or the cycloalkyl group represented byany of R₂₀₁ to R₂₀₃ may have as a substituent an alkyl group(containing, e.g., 1 to 15 carbon atoms), a cycloalkyl group(containing, e.g., 3 to 15 carbon atoms), an aryl group (containing,e.g., 6 to 14 carbon atoms), an alkoxy group (containing, e.g., 1 to 15carbon atoms), a halogen atom, a hydroxyl group or a phenylthio group.Suitable examples of such substituents include 1-12C straight-chain orbranched alkyl groups, 3-12C cycloalkyl groups and 1-12C straight-chain,branched or cyclic alkoxy groups. Of these substituents, 1-4C alkylgroups and 1-4C alkoxy groups are preferred over the others. One of R₂₀₁to R₂₀₃ may have such a substituent, or all of R₂₀₁ to R₂₀₃ may havesuch substituents. When R₂₀₁ to R₂₀₃ are aryl groups, it is preferablethat such a substituent is situated in the p-position of each arylgroup.

Next, the compound (ZI-2) is described below.

The compound (ZI-2) is a compound represented by the formula (ZI)wherein R₂₀₁ to R₂₀₃ each independently represent an organic grouphaving no aromatic ring. The term “aromatic ring” as used herein isintended to also include aromatic rings containing hetero atoms.

The number of carbon atoms in an aromatic ring-free organic group aseach of R₂₀₁ to R₂₀₃ is generally from 1 to 30, preferably from 1 to 20.

Each of R₂₀₁ to R₂₀₂ is preferably an alkyl group, a cycloalkyl group,an allyl group or a vinyl group, far preferably a straight-chain,branched or cyclic 2-oxoalkyl group, or an alkoxycarbonylmethyl group,further preferably a straight-chain or branched 2-oxoalkyl group.

The alkyl group as each of R₂₀₁ to R₂₀₃ may have either a straight-chainor a branched form, with suitable examples including 1-10Cstraight-chain and branched alkyl groups (such as a methyl group, anethyl group, a propyl group, a butyl group and a pentyl group). Thealkyl group as each of R₂₀₁ to R₂₀₃ is far preferably a straight-chainor branched 2-oxoalkyl group or an alkoxycarbonylmethyl group.

The cycloalkyl group as each of R₂₀, to R₂₀₃ is preferably a 3-10Ccycloalkyl group (such as a cyclopentyl group, a cyclohexyl group or anorbornyl group). The cycloalkyl group as each of R₂₀₁ to R₂₀₃ is farpreferably a cyclic 2-oxoalkyl group.

Suitable examples of a straight-chain, branched and cyclic 2-oxoalkylgroup as each of R₂₀₁ to R₂₀₃ include the above-recited alkyl andcycloalkyl groups having >C═O at their respective 2-positions.

The alkoxy moiety in an alkoxycarbonylmethyl group as each of R₂₀, toR₂₀₃ is preferably a 1-5C alkoxy group (such as a methoxy, ethoxy,propoxy, butoxy or pentoxy group).

Each of groups represented by R₂₀, to R₂₀₃ may further be substitutedwith a halogen atom, an alkoxy group (containing, e.g., 1 to 5 carbonatoms), a hydroxyl group, a cyano group or a nitro group.

The compound (ZI-3) is a compound represented by the following formula(ZI-3), namely a compound having a phenacylsulfonium salt structure.

In the formula (ZI-3), R_(1c) to R_(5c) each represent a hydrogen atom,an alkyl group, a cycloalkyl group, an alkoxy group or a halogen atomindependently.

R_(6c) and R_(7c) each represent a hydrogen atom, an alkyl group or acycloalkyl group independently.

R_(x) and R_(y) each represent an alkyl group, a cycloalkyl group, anallyl group or a vinyl group independently.

Any two or more of R_(1c) to R_(7c) may combine with one another to forma ring structure, and R_(x) and R_(y) may also combine with each otherto form a ring structure. In such a ring structure, an oxygen atom, asulfur atom, an ester linkage or an amide linkage may be contained. Thegroup formed by combining any two or more of R_(1c) to R_(7c) or bycombining R_(x) and R_(y) may be a butylene group or a pentylene group.

X⁻ represents a non-nucleophilic anion, and examples thereof include thesame non-nucleophilic anions as examples of X⁻ in formula (ZI).

The alkyl group as each of R_(1c) to R_(7c) may have either astraight-chain form or a branched form, and suitable examples thereofinclude 1-20C straight-chain and branched alkyl groups, preferably 1-12Cstraight-chain and branched alkyl groups (such as a methyl group, anethyl group, a straight-chain or branched propyl group, straight-chainor branched butyl groups, and straight-chain or branched pentyl groups).

Suitable examples of the cycloalkyl group as each of R_(1c) to R_(7c)include 3-8C cycloalkyl groups (such as a cyclopentyl group and acyclohexyl group).

The alkoxy group as each of R_(1c) to R_(5c) may have either astraight-chain form, or a branched form, or a cyclic form, and examplesthereof include 1-10C alkoxy groups, preferably 1-5C straight-chain andbranched alkoxy groups (such as a methoxy group, an ethoxy group, astraight-chain or branched propoxy group, straight-chain or branchedbutoxy groups, and straight-chain or branched pentoxy groups) and 3-8Ccycloalkoxy groups (such as a cyclopentyloxy group and a cyclohexyloxygroup).

It is preferable that any of R_(1c) to R_(5c) is a straight-chain orbranched alkyl group, a cycloalkyl group, or a straight-chain, branchedor cyclic alkoxy group, and it is far preferable that the number oftotal carbon atoms in R_(1c) to R_(5c) is from 2 to 15. By respond tothis request, the solvent solubility can be enhanced, and development ofparticles during storage can be inhibited.

Examples of the alkyl group as each of R_(x) and R_(y) include the samegroups as examples of the alkyl group as each of R_(1c) to R_(7c),preferably straight-chain and branched 2-oxoakyl groups andalkoxycarbonylmethyl groups.

Examples of the cycloalkyl group as each of R_(x) and R_(y) include thesame groups as examples of the cycloalkyl group as each of R_(1c) toR_(7c), preferably cyclic 2-oxoakyl groups

Examples of the straight-chain, branched and cyclic 2-oxoalkyl groupsinclude the same alkyl and cycloalkyl groups as R_(1c) to R_(7c) mayrepresent, except that they have >C═O at their respective 2-positions.

The alkoxy moiety in the alkoxycarbonylmethyl group includes the samealkoxy groups as R_(1c) to R_(5c) each may represent.

Each of R_(x) and R_(y) is preferably an alkyl group containing at least4 carbon atoms, far preferably an alkyl group containing at least 6carbon atoms, further preferably an alkyl group containing at least 8carbon atoms.

In the formulae (ZII) and (ZIII) each, R₂₀₄ to R₂₀₇ each represent anaryl group, an alkyl group or a cycloalkyl group independently.

The aryl group as each of R₂₀₄ to R₂₀₇ is preferably a phenyl group or anaphthyl group, far preferably a phenyl group.

The alkyl group as each of R₂₀₄ to R₂₀₇ may have either a straight-chainform or a branched form, with suitable examples including 1-10Cstraight-chain and branched alkyl groups (such as a methyl group, anethyl group, a propyl group, a butyl group and a pentyl group).

Suitable examples of the cycloalkyl group as each of R₂₀₄ to R₂₀₇include 3-10C. cycloalkyl groups (such as a cyclopentyl group, acyclohexyl group and a norbornyl group).

Examples of a substituent that R₂₀₄ to R₂₀₇ each may have include analkyl group (containing, e.g., 1 to 15 carbon atoms), a cycloalkyl group(containing, e.g., 3 to 15 carbon atoms), an aryl group (containing,e.g., 6 to 15 carbon atoms), an alkoxy group (containing, e.g., 1 to 15carbon atoms), a halogen atom, a hydroxyl group and a phenylthio group.

X⁻ represents a non-nucleophilic anion, and examples thereof include thesame non-nucleophilic anions as the X⁻ in the formula (ZI) represents.

As examples of preferred ones of compounds which can decompose uponirradiation with an actinic ray or radiation to generate acids,compounds represented by the following formulae (ZIV), (ZV) and (ZVI)can be further given.

In the formulae (ZIV) to (ZVI), Ar₃ and Ar₄ each represent an aryl groupindependently.

R₂₀₆ represents an alkyl group or an aryl group.

R₂₀₇ and R₂₀₈ each represent an alkyl group, an aryl group or anelectron-attracting group. R₂₀₇ is preferably an aryl group. R₂₀₈ ispreferably an electron-attracting group, far preferably a cyano group ora fluoroalkyl group.

A represents an alkylene group, an alkenylene group or an arylene group.

Of the compounds that can decompose upon irradiation with an actinic rayor radiation to generate acids, the compounds represented by (ZI) to(ZIII) are preferred over the others.

Examples of particularly preferred ones of compounds that can decomposeupon irradiation with an actinic ray or radiation to generate acids areillustrated below.

Acid generators can be used singly or as combinations of two or morethereof. When two or more types of acid generators are used incombination, it is preferable that compounds generating two types oforganic acids differing from each other by at least two in the totalnumber of atoms, except for hydrogen atoms, are used in combination.

The content of acid generators in a positive resist composition ispreferably from 0.1 to 20 mass %, far preferably from 0.5 to 10 mass %,further preferably from 1 to 7 mass %, based on the total solids in thecomposition.

[3] Fluorine-Containing Resin (C)

The positive resist composition according to the invention contains afluorine-containing resin having at least one group selected from thefollowing category (X), (XI) or (XII).

(X): Alkali-soluble groups.

(XI): Groups capable of decomposing under action of an alkali developerand increasing resin (C) solubility in an alkaline developer.

(XII): Groups capable of decomposing under action of an acid andincreasing resin (C) solubility in an alkaline developer.

(X) Alkali-Soluble Group

Examples of an alkali-soluble group include a phenolic hydroxyl group, acarboxylic group, a fluorinated alcohol group, a sulfonic acid group, asulfonamido group, a sulfonylimido group, an(alkylsulfonyl)(alkylcarbonyl)methylene group, an(alkylsulfonyl)(alkylcarbonyl)imido group, a bis(alkylcarbonyl)methylenegroup, a bis(alkylcarbonyl)imido group, a bis(alkylsulfonyl)methylenegroup, a bis(alkylsulfonyl)imido group, a tris(alkylcarbonyl)methylenegroup and a tris(alkylsulfonyl)methylene group.

Of these alkali-soluble groups, a fluorinated alcohol group (preferablya hexafluoroisopropanol group or —C(CF₃)(CF₃)(OH)), a sulfonimido groupand a bis(alkylcarbonyl)methylene group are preferred over the others.

(XI) Group Capable of Decomposing Under Action of Alkali Developer andIncreasing Resin (C) Solubility in Alkaline Developer

Examples of a group capable of decomposing under action of an alkalideveloper and increasing resin (C) solubility in an alkaline developerinclude a lactone group, an acid anhydride group and an acid imidegroup.

(XII) Group Capable of Decomposing Under Action of Acid and IncreasingResin (C) Solubility in Alkaline Developer

Examples of a group capable of decomposing under action of an acid andincreasing resin (C) solubility in an alkaline developer include thesame acid-decomposable groups as recited in the description of alicyclichydrocarbon-containing acid-decomposable resins.

In a fluorine-containing resin (C), fluorine atoms may be contained inany of groups falling under the categories (X) to (XII), or may becontained in other moieties. Fluorine atoms, though may be contained ineither main chain or side chains of the resin, are preferably containedin side chains. Additionally, fluorine atoms may be contained inrepeating units having groups falling under any of the categories (X) to(XII), or may be contained in other repeating units.

The fluorine-containing resin (C) is preferably a resin havingfluorine-containing 1-4C alkyl groups, fluorine-containing cycloalkylgroups, or fluorine-containing aryl groups.

The alkali-soluble resin (C) among fluorine-containing resins is a resinhaving alkali solubility, or a resin soluble in an alkali developer asmentioned below (an alkaline aqueous solution having a pH of 10.0 to15.0 at 23° C.).

Therefore, the alkali-soluble resin (C) has alkali-soluble groups (X)and/or groups (XI) that can decompose under action of an alkalideveloper and increase alkali developer solubility of the resin ofComponent (C).

Examples of groups (X) and (XI) include the same ones as the foregoinggroups.

The fluorine-containing 1-4C alkyl groups are 1-4C straight-chain orbranched alkyl groups which each are substituted with at least onefluorine atom and may further have another substituent.

The fluorine-containing cycloalkyl groups are mononuclear or polynuclearcycloalkyl groups which each are substituted with at least one fluorineatom and may further have another substituent.

The fluorine-containing aryl groups are aryl groups, such as a phenylgroup or a naphthyl group, which each are substituted with at least onefluorine atom and may further have another substituent.

Examples of the fluorine-containing resin (C) include resins havingrepeating units represented by any of the following formulae (C1) to(C5).

In the formulae (C1) to (C5), Rfs each represent a group having a 1-4Cfluoroalkyl group or a hydrogen atom independently.

P represents a straight-chain or branched alkylene group, or amononuclear or polynuclear cycloalkylene group, preferably a methylenegroup, an ethylene group, a cyclohexylene group, an adamantylene groupor a norbornylene group.

X represents a hydrogen atom, a halogen atom, or an alkyl group. Thealkyl group may have a straight-chain or branched form, and may alsohave a substituent, such as a halogen atom.

Q represents a single bond, an alkylene group, a divalent linkage grouphaving a mononuclear or polynuclear alicyclic hydrocarbon structure, anether group, an ester group, a carbonyl group, or a divalent groupformed by combining two or more of the groups recited above. When n is 2or 3, however, Q represents any of the groups recited above which eachare further substituted with one or two groups represented by—C(Rf)₂—OH. Q is preferably a single bond or a linkage group representedby -Q₁-CO₂—. Q₁ is a straight-chain or branched alkylene group, or amononuclear or polynuclear cycloalkylene group, preferably a methylenegroup, an ethylene group, a cyclohexylene group, an adamantylene groupor a norbornylene group.

X₁₁ represents an oxygen atom or a —N(R₁₃)— group. R₁₃ represents ahydrogen atom, a halogen atom, or an alkyl group. The alkyl group mayhave a straight-chain or branched form, and may also have a substituent,such as a halogen atom.

R₁₂ and R₂₁ each represent an organic group having at least one fluorineatom.

n represents a natural number of 1 to 3.

Suitable examples of fluorine-containing repeating units in thefluorine-containing resin (C) are illustrated below, but these examplesshould not be construed as limiting the scope of the invention.

Examples of the fluorine-containing resin (C) are illustrated below, butthese examples should not be construed as limiting the scope of theinvention.

When the fluorine-containing resin (C) is an alkali-soluble resin, theamount of alkali-soluble groups (acid groups) is preferably from 2 to 10milliequivalent/g, far preferably from 2 to 8 milliequivalent/g, interms of an acid value of the alkali-soluble resin (C). The acid valueof a compound is determined by measurement of the amount (mg) ofpotassium hydroxide required for neutralizing the compound.

The fluorine-containing resin (C) contains fluorine atoms in aproportion of preferably 5 to 80 mass %, far preferably 10 to 80 mass %,further preferably 20 to 60 mass %, based on the molecular weightthereof.

The weight-average molecular weight of the fluorine-containing resin (C)is preferably from 1,000 to 100,000, far preferably from 1,000 to50,000.

The content of residual monomers in the fluorine-containing resin (C) ispreferably from 0 to 10 mass %, far preferably from 0 to 5 mass %.Further, it is preferable to use the fluorine-containing resin (C)having a molecular weight distribution (Mw/Mn, also referred to as thedispersion degree) in the range of 1 to 5, especially 1 to 3, from theviewpoints of resolution, resist profile and sidewall of resist patternand roughness.

The amount of fluorine-containing resin (C) added to a positive resistcomposition is preferably from 0.1 to 30 mass %, far preferably from 0.1to 10 mass %, further preferably from 0.1 to 5 mass %, based on thetotal solids in the resist composition.

As to the fluorine-containing resin of Component (C),fluorine-containing resins may be used singly or as a mixture of two ormore thereof.

It is possible to utilize various commercial products as thefluorine-containing resin (C) or synthesize fluorine-containing resinsfor Component (C) in usual ways. For instance, fluorine-containingresins for Component (C) can be obtained by radical polymerization andgeneral purification as with the aforementioned synthesis of alicyclichydrocarbon-containing acid-decomposable resin.

It is natural for the fluorine-containing resin (C), as with the case ofalicyclic hydrocarbon-containing acid-decomposable resins, to be reducedin impurities including metals, and besides, it is preferable that thecontent of residual monomers and oligomer components therein is below aprescribed value, e.g., below 0.1 mass % in HPLC terms. By meeting theserequirements, the fluorine-containing resin (C) can contribute to notonly improvements in resist sensitivity, resolution, process stabilityand pattern profile but also realization of resist suffering neitherincrease in extraneous matter nor change in sensitivity with the passageof time.

[4] Solvent (D)

Examples of a solvent which can be used in dissolving each ingredienttherein to prepare a positive resist composition include organicsolvents, such as an alkylene glycol monoalkyl ether carboxylate, analkylene glycol monoalkyl ether, an alkyl lactate, an alkylalkoxypropionate, a 4-10C cyclic lactone, a 4-10C monoketone compoundwhich may contain a ring, an alkylene carbonate, an alkyl alkoxyacetateand an alkyl pyruvate.

Suitable examples of an alkylene glycol monoalkyl ether carbonateinclude propylene glycol monomethyl ether acetate, propylene glycolmonoethyl ether acetate, propylene glycol monopropyl ether acetate,propylene glycol monobutyl ether acetate, propylene glycol monomethylether propionate, propylene glycol monoethyl ether propionate, ethyleneglycol monomethyl ether acetate, and ethylene glycol monoethyl etheracetate.

Suitable examples of an alkylene glycol monoalkyl ether includepropylene glycol monomethyl ether, propylene glycol monoethyl ether,propylene glycol monopropyl ether, propylene glycol monobutyl ether,ethylene glycol monomethyl ether, and ethylene glycol ethyl ether.

Suitable examples of an alkyl lactate include methyl lactate, ethyllactate, propyl lactate, and butyl lactate.

Suitable examples of an alkyl alkoxypropionate include ethyl3-ethoxypropionate, methyl 3-methoxypropionate, methyl3-ethoxypropionate, and ethyl 3-methoxypropionate.

Suitable examples of a 4-10C. cyclic lactone include β-propiolactone,β-γ-butyrolactone, γ-butyrolactone, α-methyl-γ-butyrolactone,β-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, γ-octanoiclactone, and α-hydroxy-γ-butyrolactone.

Suitable examples of a 4-10C monoketone compound which may contain aring include 2-butanone, 3-methylbutanone, pinacolone, 2-pentanone,3-pentanone, 3-methyl-2-pentanone, 4-methyl-2-pentanone,2-methyl-3-pentanone, 4,4-dimethyl-2-pentanone,2,4-dimethyl-3-pentanone, 2,2,4,4-tetramethyl-3-pentanone, 2-hexanone,3-hexanone, 5-methyl-3-hexanone, 2-heptanone, 3-heptanone, 4-heptanone,2-methyl-3-heptanone, 5-methyl-3-heptanone, 2,6-dimethyl-4-heptanone,2-octanone, 3-octanone, 2-nonanone, 3-nonanone, 5-nonanone, 2-decanone,3-decanone, 4-decanone, 5-hexene-2-one, 3-pentene-2-one, cyclopentanone,2-methylcyclopentanone, 3-methylcyclopentanone,2,2-dimethylcyclopentanone, 2,4,4-trimethylcyclopentanone,cyclohexanone, 3-methylcyclohexanone, 4-methylcyclohexanone,4-ethylcyclohexanone, 2,2-dimethylcyclohexanone,2,6-dimethylcyclohexanone, 2,2,6-trimethylcyclohexanone, cycloheptanone,2-methylcycloheptanone, and 3-methylcycloheptanone.

Suitable examples of an alkylene carbonate include propylene carbonate,vinylene carbonate, ethylene carbonate, and butylene carbonate.

Suitable examples of an alkyl alkoxyacetate includeacetate-2-methoxyethyl, acetate-2-ethoxyethyl,acetate-2-(2-ethoxyethoxy)ethyl, acetate-3-methoxy-3-methylfutyl, andacetate-1-methoxy-2-propyl.

Suitable examples of an alkyl pyruvate include methylpyruvate, ethylpyruvate, and propyl pyruvate.

Solvents used to advantage include solvents having boiling points of130° C. or above at ordinary temperatures and under normal atmosphericpressure. Examples of such solvents include cyclopentanone,γ-butyrolactone, cyclohexanone, ethyl lactate, ethylene glycol monoethylether acetate, propylene glycol monomethyl ether acetate, ethyl3-ethoxypropionate, ethyl pyruvate, acetate-2-ethoxyethyl,acetate-2-(2-ethoxyethoxy)ethyl, and propylene carbonate.

In the invention, the solvents recited above may be used alone, or ascombinations of two or more thereof.

The solvent used in the invention may also be a mixture of a solventhaving a hydroxyl group in its structure and a solvent having nohydroxyl group.

Examples of a solvent having a hydroxyl group include ethylene glycol,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,propylene glycol, propylene glycol monomethyl ether, propylene glycolmonoethyl ether, and ethyl lactate. Of these solvents, propylene glycolmonomethyl ether and ethyl lactate are especially preferred.

Examples of a solvent having no hydroxyl group include propylene glycolmonomethyl ether acetate, ethyl ethoxypropionate, 2-heptanone,γ-butyrolactone, cyclohexanone, butyl acetate, N-methylpyrrolidone,N,N-dimethylacetamide, and dimethyl sulfoxide. Of these solvents,propylene glycol monomethyl ether acetate, ethyl ethoxypropionate,2-heptanone, γ-butyrolactone, cyclohexanone and butyl acetate arepreferred over the others. Further, propylene glycol monomethyl etheracetate, ethyl ethoxypropionate and 2-heptanone in particular are usedto advantage.

The mixing ratio (by mass) between the solvent containing a hydroxylgroup and the solvent containing no hydroxyl group is from 1/99 to 99/1,preferably from 10/90 to 90/10, far preferably from 20/80 to 60/40. Amixed solvent containing a solvent having no hydroxyl group in aproportion of 50 weight % or above is particularly preferred from theviewpoint of evenness in coating.

[5] (E): Dissolution-Inhibiting Compound that can Decompose Under Actionof Acid to Increase Solubility in Alkali Developer and has MolecularWeight of 3,000 or Below (Also Abbreviated as “Dissolution-InhibitingCompound”)

The positive resist composition according to the invention may contain adissolution-inhibiting compound that can decompose under action of anacid to increase solubility in an alkali developer and has a moleculeweight of 3,000 or below (hereinafter referred to as “a dissolutioninhibitor” also).

As dissolution inhibitors, alicyclic or aliphatic compounds havingacid-decomposable groups, such as the cholic acid derivatives containingacid-decomposable groups described in Proceeding of SPIE, 2724, 355(1996), are suitable because they causes no lowering of transmittance atwavelengths of 220 nm or below. Examples of acid-decomposable groups andthose of alicyclic structures include the same ones as recited in thedescription of the resin of Component (A).

The molecular weight of a dissolution inhibitor which can be used in theinvention is 3,000 or below, preferably from 300 to 3,000, farpreferably from 500 to 2,500.

Such a dissolution inhibitor is added in an amount of preferably 1 to 30mass %, far preferably 2 to 20 mass %, based on the total solids in thepositive resist composition.

Examples of a dissolution inhibitor are illustrated below, but theseexamples should not be construed as limiting the scope of the invention.

[6] (F): Basic Compound

For the purpose of reducing performance changes with the passage of timefrom exposure to heating, it is preferable that the positive resistcomposition according to the invention contains a basic compound.

Examples of such a basic compound include compounds having the followingstructures (A) to (E).

In the formula (A), R²⁰⁰, R²⁰¹ and R²⁰², which may be the same ordifferent, each represent a hydrogen atom, a 1-20C alkyl group, a 3-20Ccycloalkyl group or a 6-20C aryl group independently. Herein, R²⁰¹ andR²⁰² may combine with each other to form a ring. The alkyl group may bean unsubstituted one, or may have a substituent. Suitable examples of analkyl group having a substituent include 1-20C aminoalkyl groups, 1-20Chydroxyalkyl groups and 1-20C cyanoalkyl groups.

In the formula (E), R²⁰³, R²⁰⁴, R²⁰⁵ and R²⁰⁶, which may be the same ordifferent, each represent a 1-20C alkyl group.

The alkyl groups in the formulae (A) and (E) are preferablyunsubstituted alkyl groups.

Examples of such basic compounds include substituted or unsubstitutedprimary, secondary and tertiary aliphatic amines, aromatic amines,heterocyclic amines, amide derivatives, imide derivatives, andnitrogen-containing compounds having cyano groups. Of these compounds,aliphatic amines, aromatic amines and heterocyclic amines are preferredover the others. Suitable examples of substituents which those compoundsmay have include amino groups, alkyl groups, alkoxy groups, acyl groups,acyloxy groups, aryl groups, aryloxy groups, a nitro group, a cyanogroup, ester groups and lactone groups.

Examples of favorable compounds include guanidine, aminopyrrolidine,pyrazole, pyrazoline, piperazine, aminomorpholine, aminoalkylmorpholinesand piperidine, and these compounds may have substituents. Examples ofmore favorable compounds include compounds having an imidazolestructure, a diazabicyclo structure, an onium hydroxide structure, anonium carboxylate structure, a trialkylamine structure, an anilinestructure and a pyridine structure, respectively, an alkylaminederivative having a hydroxyl group and/or an ether linkage, and ananiline derivative having a hydroxyl group and/or an ether linkage.

Examples of the compound having an imidazole structure includeimidazole, 2,4,5-triphenylimidazole and benzimidazole. Examples of thecompound having a diazabicyclo structure include1,4-diazabicyclo[2.2.2]octane, 1,5-diazabicyclo[4.3.0]nona-5-ene and1,8-diazabicyclo[5.4.0]undeca-7-ene. Examples of the compound having anonium hydroxide structure include triarylsulfonium hydroxides,phenacylsulfonium hydroxides and sulfonium hydroxides having 2-oxoalkylgroups, more specifically triphenylsulfonium hydroxide,tris(t-butylphenyl)sulfonium hydroxide, bis(t-butylphenyl)iodoniumhydroxide, phenacylthiophenium hydroxide and 2-oxopropylthiopheniumhydroxide. The compound having an onium carboxylate structure is thecompound having the structure corresponding to the substitution ofcarboxylate for the anion moiety of the compound having an oniumhydroxide structure, and examples thereof include acetate,adamantane-1-carboxylate and perfluoroalkylcarboxylates. Examples of thecompound having a trialkylamine structure include tri(n-butyl)amine andtri(n-octyl)amine. Examples of the aniline compounds include2,6-diisopropylaniline and N,N-dimethylaniline. Examples of thealkylamine derivative having a hydroxyl group and/or an ether linkageinclude ethanolamine, diethanolamine, triethanolamine andtris(methoxyethoxyethyl)amine. As an example of the aniline derivativehaving a hydroxyl group and/or an ether linkage,N,N-bis(hydroxyethyl)aniline can be given.

These basic compounds are used alone or as combinations of two or morethereof.

The amount of basic compound or compounds used is generally from 0.001to 10 mass %, preferably 0.01 to 5 mass %, based on the total solids inthe positive resist composition.

As to the usage ratio of acid generator(s) to basic compound(s) in thecomposition, the acid generator/basic compound ratio (by mole)=2.5 to300 is appropriate. More specifically, it is appropriate that the ratioby mole be adjusted to at least 2.5 in point of sensitivity andresolution, while it be adjusted to at most 300 from the viewpoint ofpreventing the resolution from decreasing by thickening of resistpatterns with the passage of time from the end of exposure to heatingtreatment. The acid generator/basic compound ratio (by mole) ispreferably from 5.0 to 200, far preferably from 7.0 to 150.

[7] (G): Surfactant

It is preferable that the positive resist composition according to theinvention further contains a surfactant, specifically a surfactantcontaining at least one fluorine atom and/or at least one silicon atom(namely either a surfactant containing at least one fluorine atom, or asurfactant containing at least one silicon atom, or a surfactantcontaining both fluorine and silicon atoms), or a combination of atleast two of these surfactants.

Incorporation of such a surfactant in the positive resist compositionaccording to the invention makes it possible to provide resist patternshaving strong adhesion and reduced development defect while ensuring thecomposition both satisfactory sensitivity and high resolution in thecase of using an exposure light source of 250 nm or below, especially220 nm or below.

Examples of a surfactant containing at least one fluorine atom and/or atleast one silicon atom include the surfactants disclosed inJP-A-62-36663, JP-A-61-226746, JP-A-61-226745, JP-A-62-170950,JP-A-63-34540, JP-A-7-230165, JP-A-8-62834, JP-A-9-54432, JP-A-9-5988,JP-A-2002-277862, and U.S. Pat. Nos. 5,405,720, 5,360,692, 5,529,881,5,296,330, 5,436,098, 5,576,143, 5,294,511 and 5,824,451. In addition,the following commercially available surfactants can be used as theyare.

Examples of commercial surfactants which can be used includefluorine-containing surfactants, such as EFTOP EF301 and EF303 (producedby Shin-Akita Kasei K.K.), Florad FC430, 431 and 4430 (produced bySumitomo 3M, Inc.), Megafac F171, F173, F176, F189, F113, F110, F177,F120 and R₀₈ (produced by Dainippon Ink & Chemicals, Inc.), SurflonS-382, SC101, 102, 103, 104, 105 and 106 (produced by Asahi Glass Co.,Ltd.), Troysol S-366 (produced by Troy Chemical Industries, Inc.), GF300and GF-150 (produced by Toagosei Co., Ltd.), Surflon S-393 (produced bySeimi Chemical Co., Ltd.), EFTOP EF121, EF122A, EF122B, RF122C, EF125M,EF135M, EF351, EF352, EF801, EF802 and EF601 (produced by JEMCO Inc.),PF636, PF656, PF6320 and PF6520 (produced by OMNOVA Solutions Inc.), andFTX-208G, 218G, 230G, 204D, 208D, 212D, 218D and 222D (produced byNEOS), or silicon-containing surfactants. Additionally, organosiloxanepolymer KP-341 (produced by Shin-Etsu Chemical Co., Ltd.) can be used asa silicon-containing surfactant.

In addition to known surfactants as recited above, the surfactantsusable in the invention include surfactants using polymers containingfluorinated aliphatic groups derived from fluorinated aliphaticcompounds synthesized by a telomerization method (also referred to as atelomer method) or an oligomerization method (also referred to as anoligomer method). These fluorinated aliphatic compounds can besynthesized according to the methods disclosed in JP-A-2002-90991.

The polymers containing fluorinated aliphatic groups are preferablycopolymers of fluorinated aliphatic group-containing monomers andpoly(oxyalkylene) acrylates and/or poly(oxyalkylene) methacrylates,wherein the fluorinated aliphatic group-containing units may bedistributed randomly or in blocks. Examples of such poly(oxyalkylene)groups include a poly(oxyethylene) group, a poly(oxypropylene) group anda poly(oxybutylene) group. In addition, the poly(oxyalkylene) groups maybe units containing alkylene groups of different chain lengths in theirrespective oxyalkylene chains, such as poly(oxyethyleneblock-oxypropylene block-oxyethylene block combination) andpoly(oxyethylene block-oxypropylene block combination). Further, thecopolymers of fluorinated aliphatic group-containing monomers andpoly(oxyalkylene) acrylates (or methacrylates) may be binary copolymersor at least ternary copolymers prepared by copolymerizing at least twodifferent kinds of fluorinated aliphatic group-containing monomers andat least two different kinds of poly(oxyalkylene) acrylates (ormethacrylates) at the same time.

Examples of commercially available surfactants of such types includeMegafac F178, F-470, F-473, F-475, F-476 and F-472 (produced byDainippon Ink & Chemicals, Inc.). Additional examples of surfactants ofsuch types include a copolymer of C₆F₁₃ group-containing acrylate (ormethacrylate) and poly(oxyalkylene) acrylate (or methacrylate), and aterpolymer of C₃F₇ group-containing acrylate (or methacrylate),poly(oxyethylene)acrylate (or methacrylate) andpoly(oxypropylene)acrylate (or methacrylate).

On the other hand, surfactants other than the surfactants which eachcontain at least one fluorine atom and/or at least one silicon atom canalso be used in the invention. Examples of such surfactants includenonionic surfactants, such as polyoxyethylene alkyl ethers (e.g.,polyoxyethylene lauryl ether, polyoxyethylene stearyl ether,polyoxyethylene cetyl ether, polyoxyethylene oleyl ether),polyoxyethylene alkyl aryl ethers (e.g., polyoxyethylene octyl phenolether, polyoxyethylene nonyl phenol ether),polyoxyethylene-polyoxypropylene block copolymers, sorbitan fatty acidesters (e.g., sorbitan monolaurate, sorbitan monopalmitate, sorbitanmonostearate, sorbitan monooleate, sorbitan trioleate, sorbitantristearate), and polyoxyethylene sorbitan fatty acid esters (e.g.,polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitanmonopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylenesorbitan trioleate, polyoxyethylene sorbitan tristearate).

These surfactants may be used alone, or as combinations of two or morethereof.

The amount of surfactants used is preferably from 0.01 to 10 mass %,preferably 0.1 to 5 mass %, based on the total ingredients (exclusive ofa solvent) in the positive resist composition.

[8] (I): Alkali-Soluble Resin

The positive resist composition according to the invention can furthercontain a resin that has no acid-decomposable group and is insoluble inwater but soluble in an alkaline developer, and thereby the sensitivitycan be increased.

In the invention, novolak resins having molecular weight of the order of1,000 to 20,000 and poly(hydroxystyrene) derivatives having molecularweight of the order of 3,000 to 50,000 can be used as the alkali-solubleresin of the foregoing type. However, since those resins absorb lightwith wavelengths of 250 nm or below to a great extent, it is preferablethat they are used in a partially hydrogenated state or in proportion of30 weight % or below to the total resins.

In addition, resins containing carboxyl groups as alkali-soluble groupscan also be used. For the purpose of enhancing dry-etching resistance,it is advantageous for the resins to contain mononuclear or polynuclearalicyclic hydrocarbon groups. Examples of such resins include copolymersof methacrylic acid and methacrylic acid esters showing noacid-decomposability and having alicyclic hydrocarbon structures, andalicyclic hydrocarbyl(meth)acrylate resins having carboxyl groups attheir terminals.

[9] (I): Onium Carboxylate

The positive resist composition according to the invention may furthercontain an onium carboxylate. Examples of such an onium carboxylateinclude sulfonium carboxylates, iodonium carboxylates and ammoniumcarboxylates. Of these onium salts, iodonium salts and sulfonium saltsare especially preferred. In addition, it is preferable that neitheraromatic groups nor carbon-carbon double bonds are contained in thecarboxylate residues of onium carboxylates which may be used in theinvention. Examples of an especially preferable anion moiety include1-30C straight-chain and branched alkyl carboxylate anions andmononuclear or polynuclear cycloalkyl carboxylate anions. Of theseanions, those preferred by far are the carboxylate anions whose alkylgroups are partially or entirely substituted by fluorine atoms. Inaddition, those alkyl chains may contain oxygen atoms. By containing anonium salt having such a carboxylate anion, the resist composition canensure transparency to light with wavelengths of 220 nm or below, andcan have increased sensitivity and resolution and improved pitchdependency and exposure margin.

Examples of a fluorinated carboxylate anion include fluoroacetate anion,difluoroacetate anion, trifluoroacetate anion, pentafluoropropionateanion, heptafluorobutyrate anion, nanofluoropentanate anion,perfluorododecanate anion, perfluorotridecanate anion,perfluorocyclohexanecarboxylate anion and2,2-bistrifluoromethylpropionate anion.

These onium carboxylates can be synthesized by allowing sulfoniumhydroxide, iodonium hydroxide or ammonium hydroxide and carboxylic acidsto react with silver oxide in an appropriate solvent.

The suitable content of onium carboxylate in the resist composition isfrom 0.1 to 20 mass %, preferably from 0.5 to 10 mass %, far preferablyfrom 1 to 7 mass %, on a solids basis.

Other Additives

The positive resist composition according to the invention can furthercontain, on an as needed basis, dyes, plasticizers, photosensitizers,light absorbents, and compounds which can further dissolution indevelopers (e.g., phenol compounds having molecular weights of 1,000 orbelow, alicyclic or aliphatic compounds having carboxyl groups).

Syntheses of such phenol compounds 1,000 or below in molecular weightare easy for persons skilled in the art by reference to the methods asdisclosed in JP-A-4-122938, JP-A-2-28531, U.S. Pat. No. 4,916,210 andEuropean Patent No. 219,294.

Examples of alicyclic and aliphatic compounds having carboxyl groupsinclude carboxylic acid derivatives having steroid structures, such ascholic acid, deoxycholic acid and lithocholic acid, adamantanecarboxylicacid derivatives, adamantanedicarboxylic acid, cyclohexanecarboxylicacid and cyclohexanedicarboxylic acid, but not limited to the compoundsrecited above.

[Physical Properties of Positive Resist Composition]

From the viewpoint of improvement in resolution, it is favorable thatthe positive resist composition according to the invention is used in acoating thickness of 30 to 250 nm, preferably 30 to 200 nm. The coatingthickness in such a range can be attained by imparting just rightviscosity to the positive resist composition through adjustment of thesolids concentration in the composition to an appropriate range, andperforming enhancements of coating suitability and film formability.

The concentration of total solids in the positive resist composition isgenerally from 1 to 10 mass %, preferably from 1 to 8 mass %, farpreferably from 1.0 to 7.0 mass %.

[Preparation of Positive Resist Composition]

The positive resist composition according to the invention is preparedby dissolving the ingredients as described above in a specified solvent,preferably the mixed solvent as described above, and passing theresulting solution through a filter. The filter suitably used forfiltering is a polytetrafluoroethylene, polyethylene or nylon filtercapable of filtering to 0.1 microns or below, preferably 0.05 microns orbelow, far preferably 0.03 microns or below.

[Pattern Forming Method]

The pattern forming method of the invention is described below indetail.

As a result of our intensive study of what gives rise to deteriorationin resolution, which is traceable to topple of resist patterns, andsensitivity decrease when a chemical amplification resist is applied toimmersion lithography, we have narrowed it down to immersion liquidpermeation into a resist coating which occurs while the resist coatingmaintains contact with the immersion liquid, thereby achieving theinvention.

The image forming method of the invention has steps of:

(i) applying the positive resist composition according to the inventionto a substrate to form a resist coating,

(ii) exposing the resist coating to light via an immersion liquid,

(iii) removing the immersion liquid remaining on the resist coating,

(iv) heating the resist coating, and

(v) developing the resist coating,

and is distinguished by having the step (iii) of removing the immersionliquid remaining on the resist coating after the step (ii) of exposingthe resist coating to light via the immersion liquid and before the step(iv) of heating the resist coating.

Incidentally, the step (iv) of heating the resist coating is a stepcorresponding to the heating step generally performed after exposure andbefore development for the purpose of promoting conversion ofalkali-insoluble groups in a resist coating to alkali-soluble groups,namely the step referred to as PEB (Post Exposure Bake).

Reaction for converting alkali-insoluble groups in a chemicalamplification resist to alkali-soluble groups occurs at the time of PEBgenerally carried out during or after exposure, so reactions under PEBare important.

Although it was thought that water as the most suitable immersion liquidin the case of using ArF excimer laser is less prone to permeate into aresist coating for ArF excimer laser use since the resist coating isgenerally formed from resin and organic molecules, we have found thatminute quantities of water actually permeated into upper part of theresist coating. When the water permeates into the resist coating theresist coating surface and the vicinity of the interface between theresist coating and the substrate come to differ in water content tocause changes in diffusion distance of a generated acid and rate ofconversion reaction from alkali-insoluble groups into alkali-solublegroups, thereby resulting in unevenness of chemical reaction in thespace between the surface and the bottom of the resist coating.Therefore, there is a possibility that resist patterns of good qualitycannot be obtained.

In the case of immersion lithography using exposure wavelengths otherthan the wavelength of ArF, it is also conceivable that minutequantities of immersion liquid will permeate into a resist coating, andthere is a high possibility that resist patterns formed will becomeunsatisfactory.

A feature of the invention consists in that the step (iii) of removingthe immersion liquid remaining on a resist coating is carried out beforethe step (iv) of heating the resist coating, or PEB, and therebyreaction for converting alkali-insoluble groups into alkali-solublegroups is made uniform throughout the coating to result in formation ofsatisfactory resist patterns.

As the step (iii) of removing the immersion liquid remaining on a resistcoating, it is possible to adopt (iii-1) a step of removing theimmersion liquid by spinning the substrate, (iii-2) a step of removingthe immersion liquid by heating the substrate at temperatures on a levelthat there occurs no conversion from alkali-insoluble groups intoalkali-soluble groups, or (iii-3) a step of removing the immersionliquid by blowing a gas from a nozzle. These steps can be performed byuse of general apparatus for manufacturing semiconductors, liquidcrystal displays and devices like thermal heads, so they don't requireintroduction of new devices and are practical in point of costadvantage. Alternatively, a device permitting hot-air drying may beinstalled in an exposure apparatus or a developing machine, and the hotair generated thereby may be used for drying the remaining immersionliquid.

In the step (iii-1) of removing the immersion liquid by spinning asubstrate, the number of revolutions of the substrate is preferably 500rpm or above since the low revs cannot induce a high velocity of airflow on the resist coating surface to result in prolongation of drying.The higher revs are favorable since they can make the drying time theshorter and thereby the higher throughput can be attained.

However, the setting of the revs is generally below the upper limitdesignated by the device used. So, for instance, the revs is generallyadjusted to 3,000 rpm or below in the case of spinning a 12-inchcircular silicon-wafer substrate or 4,000 rpm or below in the case ofspinning an 8-inch circular wafer substrate.

For completion of the drying, it is appropriate that the spinning timeof the substrate be adjusted to 5 seconds or longer, and the longer thebetter. However, with the intention of minimizing throughput penalty,the setting of the spinning time may be done with consideration given tothe total time and number of devices required for other steps, such asexposure, PEB and development.

In order to eliminate the vaporized immersion liquid from apparatus, itis preferable that the apparatus is ventilated, and the ventilationpressure is preferably 20 Pa or above.

Although the device for spinning a substrate may be any device so longas it has a mechanism for spinning the substrate, a developing apparatusas general apparatus for manufacturing semiconductors, liquid crystaldisplays and devices like thermal heads is used to advantage from theviewpoint of simplicity in delivery of a substrate from exposureapparatus to developing apparatus, but the device should not beconstrued as being limited to such apparatus.

In the step (iii-2) of removing the immersion liquid by baking (heating)a resist coating, conversion of alkali-insoluble groups in the resininto alkali-soluble groups during the bake for removal of the immersionliquid allows chemical reaction to occur in a state that the immersionliquid is present in the resist coating, and raises the possibility ofrendering the chemical reaction uneven in the space between the surfaceand bottom of the resist coating. Therefore, it is appropriate that thebake temperature be adjusted to temperatures at which thealkali-insoluble groups in the resin cannot be converted intoalkali-soluble ones.

Further, it is required that the bake temperature be a temperature atwhich no conversion from alkali-insoluble groups into alkali-solublegroups is caused in the resist resin.

The temperature at which an alkali-insoluble group is converted into analkali-soluble group differs depending on the kind of resist,commercially available resists have their recommended post-baketemperatures (namely the foregoing PEB temperatures), and they aregenerally in the range of 90-150° C. At temperatures higher than therecommended temperatures, the conversion reaction from alkali-insolublegroups into alkali-soluble groups occurs with efficiency.

Accordingly, it is preferable to choose the bake temperature for removalof immersion liquid from the temperatures at least 20° C. lower than theheating temperature in the step (iv) of heating the resist coating asthe temperature at which alkali-insoluble groups cannot be convertedinto alkali-soluble groups.

The temperature required at the minimum differs depending on the kind ofimmersion liquid, and there is a high possibility of adopting water asan immersion liquid in immersion lithography utilizing ArF excimerlaser. When water is used as an immersion liquid under thesecircumstances, the heating at a temperature of 40° C. or above ispreferred. However, the immersion liquid should not be construed asbeing limited to water.

Since a short heating time cannot complete the removal of immersionliquid and a long heating time affects throughput, the heating time ispreferably adjusted to the range of 10-120 seconds.

Further, it is preferable that the apparatus is ventilated for thepurpose of eliminating the vaporized immersion liquid from apparatus,and the ventilation pressure is preferably 3 Pa or above. As to thedevice for heating the substrate, although any devices may be used asfar as they have a heating mechanism, it is advantageous to use aheating unit attendant on a developing apparatus as general apparatusfor manufacturing semiconductors, liquid crystal displays and deviceslike thermal heads from the viewpoint of simplicity in delivery of asubstrate from the exposure apparatus to the developing apparatus, butthe device should not be construed as being limited to such unit.

As another example of the step (iii) of removing the immersion liquidremaining on a resist coating, a step of feeding a water-miscibleorganic solvent to the resist coating surface for the removal can begiven.

Examples of a water-miscible organic solvent usable therein includealcohol solvents, such as methyl alcohol, ethyl alcohol, n-propylalcohol and isopropyl alcohol. Of these solvents, isopropyl alcohol ispreferred over the others.

A water-miscible organic solvent may be fed onto a wafer surface via adropping nozzle under a condition that the wafer is made to adsorb to aholding mount by means of a vacuum chuck. It is preferable that thesolvent feeding is carried out in an amount of 0.1 to 2.0 kg/cm² so asto distribute the solvent over the whole surface of the wafer. Thesolvent feeding may be performed in a state that the wafer is standingstill, or it may be performed as the water is rotated at a low speed(e.g., 30 rpm). After the solvent feeding is stopped, the water-miscibleorganic solvent may be dried by ventilation as the wafer is in astationary state, or by spinning the wafer at 1,000 rpm or above.

The amount of immersion liquid remaining in the resist coating aftercompletion of the step (iii) of removing the immersion liquid remaininga resist coating is preferably 0.1 mass % or below, far preferably 0.01mass % or below.

As a method for measuring a water content in the case of using water ora water solution as the immersion liquid, there is known the method ofscraping the resist coating away from the substrate by use of, e.g., aspatula and measuring its water content with a Karl Fischer MoistureTitrator (MKS-500, made by Kyoto Electronics Manufacturing Co., Ltd.).In the case where the immersion liquid is a non-aqueous solution, on theother hand, there is known the method of dissolving the resist coatingscraped away from the substrate in a solvent, such as cyclohexanone, anddetermining the liquid content by gas chromatography (using, e.g., GC-17Aver. 3, made by Shimadzu Corporation).

In the pattern forming method of the invention, the step (i) of applyinga positive resist composition to the substrate to form a resist coating,the step (ii) of exposing the resist film via an immersion liquid, thestep (iv) of heating the resist coating and the step (v) of developingthe resist coating can be performed using generally known methods.

At the removal of the immersion liquid remaining on the resist coating,it is preferable that a liquid film (puddle) of the immersion liquid(preferably purified water) is formed on the resist coating, and thenthe liquid film is removed so as not to left any liquid drops.

By utilizing the surface tension of the immersion liquid, the puddle maybe formed by putting the immersion liquid on the resist coating as thewafer is kept still.

In the invention, it is preferable that the surface of the resistcoating is cleaned prior to the step (ii) of exposing the resist coatingvia the immersion liquid.

The cleaning is performed by bringing a liquid to contact with theresist coating surface and eliminating dirt and particles.

As the liquid brought into contact with the resist coating surface, theimmersion liquid may be used, or a liquid for cleaning, other than theimmersion liquid, may be used.

The heating of the resist coating in the step (iii-2) and the step (iv)is generally carried out by heating the substrate having the resistcoating by means of a hot plate.

After heating the resist coating in the step (iv), the resist coating isgenerally cooled to the vicinity of room temperature (e.g., 23° C.), andthen undergoes development in the step (v).

The wavelength of a light source used in exposure apparatus forimmersion lithography has no particular limitations in the invention,but a start has been made in studying of immersion lithography at thewavelengths of ArF excimer laser (193 nm) and F₂ excimer laser, and theinvention can be applied to both wavelengths.

The liquid suitable as immersion liquid is transparent to exposurewavelengths, and the refractive index thereof preferably has thesmallest possible temperature coefficient so that the distortion ofoptical images projected onto the resist coating is minimized. In thecase where the exposure light source is ArF excimer laser (wavelength:193 nm) in particular, it is preferable to use water from the viewpointsof availability and easiness of handling in addition to the aforesaidviewpoints.

When water is used as the immersion liquid, an additive (liquid) capableof reducing the surface tension of water and enhancing the surfaceactivity may be added in a slight proportion. This additive ispreferably a liquid not causing dissolution of the coating layer on thewafer and having a negligibly small effect on an optical coat providedon the underside of lens element.

Suitable examples of such an additive include aliphatic alcoholcompounds having almost the same refractive indexes as that of water,such as methyl alcohol, ethyl alcohol and isopropyl alcohol. Addition ofalcohol having almost the same refractive index as that of water canoffer an advantage that a change in refractive index as the liquid inits entirety can be made minimal even when the alcohol concentration inthe immersion liquid is altered by vaporization of the alcohol.

On the other hand, mixing of a substance opaque to light of 193 nm andan impurity greatly differing in refractive index from water bringsabout distortion of optical images projected onto the resist, so thewater used is preferably distilled water. Further, purified water havingundergone filtration by passage through an ion exchange filter may beused.

The substrate on which the resist coating is formed has no particularrestriction in the invention, and it is possible to use an inorganicsubstrate, such as silicon, SiN, SiO₂ or SiO₂/SiN; a coating-typeinorganic substrate, such as SOG; or a substrate generally used in alithographic process for manufacturing semiconductors, such as ICs,circuit boards for LCDs and thermal heads, and for photofabrication ofother devices. Further, an organic antireflective film may be formedbetween the resist coating and the substrate, if needed.

Examples of an alkali developer used in the step of carrying outdevelopment include aqueous alkaline solutions of inorganic alkalis,such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodiumsilicate, sodium metasilicate and aqueous ammonia, primary amines, suchas ethyl amine and n-propylamine, secondary amines, such as diethylamineand di-n-butylamine, tertiary amines, such as triethylamine andmethyldiethylamine, alcohol amines, such as dimethylethanolamine andtriethanolamine, quaternary ammonium salts, such as tetramethylammoniumhydroxide and tetraethylammonium hydroxide, and cyclic amines, such aspyrrole and piperidine.

Further, it is possible to use the alkaline aqueous solution as recitedabove to which an alcohol compound and a surfactant are added inappropriate amounts.

The alkali concentration in an alkali developer is generally from 0.1 to20 mass %.

The pH of the alkali developer is generally from 10.0 to 15.0.

As a rinse solution, purified water is used, but thereto an appropriateamount of surfactant may also be added.

After the development-processing or the processing with a rinsesolution, treatment for eliminating the developer or the rinse solutionadhering to patterns by use of a supercritical liquid can further beperformed.

EXAMPLES

The invention will now be illustrated in greater detail by reference tothe following examples, but these examples should not be construed aslimiting the scope of the invention in any way.

The structures of alicyclic hydrocarbon-containing acid-decomposableresins (1) to (24) used in Examples and Comparative Examples areillustrated below. In addition, the compositions (which each areexpressed in a ratio between proportions (by mole %) of repeating unitsarranged in the direction from the left to the right in each individualstructural formula), weight-average molecular weights (Mw) anddispersion degrees (Mw/Mn) of the alicyclic hydrocarbon-containingacid-decomposable resins (1) to (24) are shown in the following Tables 1and 2.

TABLE 1 Resin Composition Mw Mw/Mn 1 39/20/41 9,800 1.9 2 40/22/3812,000 2.0 3 34/33/33 11,000 2.3 4 45/15/40 10,500 2.1 5 35/15/50 6,7002.2 6 30/25/45 8,400 2.3 7 39/20/41 10,500 2.1 8 49/10/41 9,500 2.5 935/32/33 14,000 2.6 10 35/35/30 6,700 2.3 11 40/22/38 8,500 2.5 1240/20/35/5 12,500 2.4 13 50/50 14,000 1.9 14 40/15/40/5 10,000 1.8 1550/50 8,300 1.5 16 40/15/40/5 9,800 2.3 17 50/50 5,200 2.1 18 35/20/40/56,100 2.3 19 30/30/30/10 8,600 2.5 20 40/20/35/5 12,000 2.1

TABLE 2 Resin Composition Mw Mw/Mn 21 50/10/40 10,000 1.2 22 40/20/409,600 1.4 23 40/20/30/10 10,400 1.1 24 45/20/30/5 9,900 1.3

Synthesis Example 1 Syntheses of Resins (C-1) and (C-2)

3,5-Bis(1,1,1,3,3,3-hexafluoro-2-hydroxypropane-2-yl)cyclohexyl2-trifluoromethylmethacrylate in an amount of 0.06 mole and(5-norbornene-2-methyl)-1,1,1,3,3,3-hexafluoropropane-2-ol in an amountof 0.04 mole were prepared, and mixed. This mixture was placed in anatmosphere of nitrogen and stirred at 80° C., and thereto 1.5 mole % ofV-59, a polymerization initiator produced by Wako Pure ChemicalIndustries, Ltd., was added and stirred for additional 3 hours.Thereafter, the stirring was further continued for 12 hours while adding1.5 mole % of the polymerization initiator V-59 at intervals of 3 hours.After completion of the reaction, the reaction solution (C-1) wasdissolved in 20 mL of THF, and cooled to room temperature. The resultingsolution was poured into 800 mL of hexane to result in precipitation ofwhite powdery crystals. These crystals were filtered off, therebycollecting the intended resin (C-1) having the structure illustratedhereinafter.

The polymer's compositional ratio (by mole %) determined by ¹H-NMR was60/40 (corresponding to the arranging order (in the direction from theleft to the right) of repeating units in the structural formula, as werethe compositional ratios mentioned below). Further, the weight-averagemolecular weight of Resin (C-1) was found to be 8,800 as measured by GPCand calculated in terms of polystyrene, and the dispersion degree(Mw/Mn) was found to be 1.5.

Resin (C-2) having the structure illustrated hereinafter was synthesizedin the same manner as the above, except that one of the monomers wasreplaced with a different one and the ratio between the amounts ofmonomers prepared was changed to 70/30 (by mole). The compositionalratio (by mole %) of Resin (C-2) determined by ¹H-NMR was 68/32.Further, the weight-average molecular weight of Resin (C-2) was found tobe 11,000 as measured by GPC and calculated in terms of polystyrene, andthe dispersion degree (Mw/Mn) was found to be 1.7.

Synthesis Example 2 Synthesis of Resin (C-3)

Di-μ-chlorosyl-[(η-allyl)palladium(II)] in an amount of 0.262 g andsilver antimonate in an amount of 0.488 g were dissolved in 44 mL ofchlorobenzene, and stirred at room temperature. After a lapse of 20minutes, the reaction mixture was filtered, and the filtrate was addedto a mixture of 20 g of 5-norbornene-1,1,1,3,3,3-hexafluoropropane-2-ol,0.2 mL of water and 170 mL of chlorobenzene. The resulting admixture wasfurther stirred for 20 hours at room temperature, and poured into 1,200mL of methanol. A resin thus precipitated was filtered off. The resinobtained was dissolved in 150 mL of chlorobenzene, and thereto 30 ml ofmethanol and 3.2 g of sodium boron hydride were added and stirred for 3hours at room temperature. Further, the resulting reaction mixture wasallowed to stand for 24 hours at room temperature. Pd(0) grains thusprecipitated were filtered out, and the filtrate was poured into 800 mLof methanol. The thus precipitated resin was filtered off, therebygiving the intended Resin (C-3) having the structure illustratedhereinafter.

The weight-average molecular weight of Resin (C-3) was found to be 8,000as measured by GPC and calculated in terms of polystyrene, and thedispersion degree (Mw/Mn) was found to be 1.4.

Synthesis Example 3 Syntheses of Resins (C-4) to (C-6)

1,1,1,3,3,3-Hexafluoro-2-(4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropane-2-yl)cyclohexyl)propane-2-ylmethacrylate in an amount of 20 g was dissolved in 70 mL of propyleneglycol monomethyl ether acetate. To this solution, 3 mole % of apolymerization initiator V-601 produced by Wako Pure ChemicalIndustries, Ltd. was added. The resulting solution was added dropwiseover a period of 6 hours to 10 ml of propylene glycol monomethyl etheracetate heated to 80° C. After conclusion of the addition, the reactionsolution was stirred for 2 hours. The thus obtained reaction solution(C-4) was cooled to room temperature after completion of the reaction,and was poured into a 4.5-times amount of hexane to result inprecipitation of white powdery crystals. These crystals were filteredoff, thereby collecting the intended resin (C-4) having the structureillustrated hereinafter.

The weight-average molecular weight of Resin (C-4) was found to be 8,500as measured by GPC and calculated in terms of polystyrene, and thedispersion degree (Mw/Mn) was found to be 1.4.

Resin (C-5) having the structure illustrated hereinafter was synthesizedin the same manner as the above, except that the monomer was replacedwith different ones and the ratio between the amounts of monomersprepared was changed to 80/20 (by mole). In addition, the solvent usedfor crystallization was changed to methanol. The compositional ratio (bymole %) of Resin (C-5) determined by ¹H-NMR was 80/20. Further, theweight-average molecular weight of Resin (C-5) was found to be 13,000 asmeasured by GPC and calculated in terms of polystyrene, and thedispersion degree (Mw/Mn) was found to be 2.1.

Resin (C-6) having the structure illustrated hereinafter was synthesizedin the same manner as Resin (C-4), except that a different monomer wasfurther added and the ratio between the amounts of monomers prepared waschanged to 70/30 (by mole). In addition, the solvent used forcrystallization was changed to methanol. The compositional ratio (bymole %) of Resin (C-6) determined by ¹H-NMR was 70/30. Further, theweight-average molecular weight of Resin (C-6) was found to be 18,000 asmeasured by GPC and calculated in terms of polystyrene, and thedispersion degree (Mw/Mn) was found to be 2.3.

Synthesis Example 4 Synthesis of Resin (C-7)

Resin (C-7) having the structure illustrated hereinafter was synthesizedin the same manner as in Synthesis Example 1, except that the monomerswere replaced with different ones and the ratio between the amounts ofmonomers prepared was changed to 50/50 (by mole). In addition, thesolvent used for crystallization was changed to methanol. Thecompositional ratio (by mole %) of Resin (C-7) determined by ¹H-NMR was50/50. Further, the weight-average molecular weight of Resin (C-7) wasfound to be 5200 as measured by GPC and calculated in terms ofpolystyrene, and the dispersion degree (Mw/Mn) was found to be 1.9.

Synthesis Example 5 Synthesis of Resin (C-8)

Resin (C-8) having the structure illustrated hereinafter was synthesizedin the same manner as in Synthesis Example 3, except that the monomerwas replaced with different ones and the ratio between the amounts ofmonomers prepared was changed to 50/50 (by mole). In addition, thesolvent used for crystallization was changed to methanol. Thecompositional ratio (by mole %) of Resin (C-8) determined by ¹H-NMR was50/50. Further, the weight-average molecular weight of Resin (C-8) wasfound to be 10,200 as measured by GPC and calculated in terms ofpolystyrene, and the dispersion degree (Mw/Mn) was found to be 2.2.

Synthesis Example 6 Synthesis of Resin (C-9)

Resin (C-9) having the structure illustrated hereinafter was synthesizedin the same manner as in Synthesis Example 3, except that the monomerwas replaced with different ones and the ratio between the amounts ofmonomers prepared was changed to 60/40 (by mole). The solvent used forcrystallization was hexane. The compositional ratio (by mole %) of Resin(C-8) determined by ¹H-NMR was 60/40. Further, the weight-averagemolecular weight of Resin (C-8) was found to be 7,200 as measured by GPCand calculated in terms of polystyrene, and the dispersion degree(Mw/Mn) was found to be 2.2.

Synthesis Example 7 Synthesis of Resin (C-10)

Resin (C-10) having the structure illustrated below was synthesized inthe same manner as in Synthesis Example 1, except that the monomers werereplaced with different ones and the ratio between the amounts ofmonomers prepared was changed to 30/30/40 (by mole). In addition, thesolvent used for crystallization was changed to methanol. Thecompositional ratio (by mole %) of Resin (C-10) determined by ¹H-NMR was32/32/36. Further, the weight-average molecular weight of Resin (C-8)was found to be 5,600 as measured by GPC and calculated in terms ofpolystyrene, and the dispersion degree (Mw/Mn) was found to be 2.0.

Examples 1 to 20 and Comparative Examples 1 to 3 <Preparation of Resist>

Positive resist compositions were each prepared by dissolvingingredients in solvents as shown in the following Tables 3 and 4 so asto prepare a resist solution having a solids concentration of 7 mass %and passing the resist solution through a 0.1-μm polyethylene filter.Patterns were formed using each of the thus prepared positive resistcompositions in accordance with a method chosen from those described inTables 5 and 6, and evaluated by the following method. Results obtainedare shown in Tables 3 and 4.

[Evaluation of Development Defect]

A defect inspection system, KLA2360 (trade name, made by KLA-TencorCorporation), was used, and measurements with the inspection system weremade in a random mode under a setting that the pixel size was 0.16 μmand the threshold was 20. Specifically, development defects extractedfrom discrepancies developing by superposing images for comparison uponpixel units were detected, and the number of development defects perunit area was calculated.

TABLE 3 Composition Acid Basic Pattern Number of Resin (A) generatorResin (C) Solvent (ratio compound Surfactant forming defects (perExample 2 g (mg) (mg) by mass) (mg) (mg) method cm²) 1 1 z2  C-1SL-1/SL-2 N-5 W-1 (A) 0.14  (80) (2) (60/40) (7) (3) 2 2 z51 C-2SL-2/SL-4/SL-6 N-6 W-4 (A) 0.12 (100) (2) (40/59/1) (10) (3) 3 3 z2/z62C-1 SL-2/SL-4 N-3 W-6 (A) 0.11  (20/100) (2) (70/30) (6) (3) 4 4 z55/z65C-1 SL-2/SL-4 — — (A) 0.10  (20/100) (5) (60/40) 5 5 z55/z51 C-2SL-3/SL-4 N-6 W-6 (A) 0.15 (20/80) (1) (30/70) (10)  (4) 6 6 z44/z65 C-3SL-2/SL-4/SL-5 N-1 W-6 (B) 0.11 (25/80) (5) (40/58/2) (7) (4) 7 7z55/z47 C-2 SL-1/SL-2 N-4 W-6 (A) 0.10 (30/60) (10)  (60/40) (13) (4) 88 z65 C-4 SL-1/SL-2 N-3 W-2 (B) 0.15 (100) (3) (60/40) (6) (3) 9 9z44/z65 C-3 SL-2/SL-4/SL-6 N-2 W-3 (A) 0.14 (50/50) (3) (40/59/1) (9)(3) 10 10 z51 C-6 SL-2/SL-4 N-5 W-5 (A) 0.15 (100) (3) (70/30) (7) (3)11 11 z55/z65 C-5 SL-2/SL-4 N-1 W-4 (A) 0.16 (40/60) (3) (60/40) (7) (3)12 12 z55/z65 C-1 SL-1/SL-2 N-3 W-1 (A) 0.15 (20/80) (3) (50/50) (6) (3)13 13 z37 C-5 SL-1/SL-2 N-5 W-1 (A) 0.14 (110) (2) (30/70) (7) 5 14 14z62 C-3 SL-2/SL-4/SL-6 N-1 W-4 (A) 0.12 (120) (2) (40/59/1) (7) (5) 1515 z55/z51 C-2 SL-2/SL-4 N-3 W-6 (A) 0.11 (40/60) (2) (60/40) (6) (5)

TABLE 4 Composition Acid Basic Pattern Number of Resin (A) generatorResin (C) Solvent compound Surfactant forming defects (per 2 g (mg) (mg)(ratio by mass) (mg) (mg) method cm²) Example 16 16 z65/z9 C-3 SL-2/SL-4— W-1 (A) 0.10 (100/10) (3) (60/40) (5) 17 17 z66 C-1 SL-1/SL-2 N-5 W-1(A) 0.15 (100)  (2) (60/40) (7) (5) 18 18 z16 C-4 SL-2/SL-4/SL-6 N-6 W-4(A) 0.14 (90) (2) (40/59/1) (10)  (5) 19 19 z55 C-2 SL-2/SL-4 N-3 W-6(A) 0.15 (80) (3) (70/30) (6) (5) 20 20 z51 C-1 SL-2/SL-4 — — (A) 0.16(100)  (2) (70/30) Comparative Example  1 1 z2  — SL-1/SL-2 (60/40) N-5W-1 (A) 2.46 (80) (7) (5)  2 1 z2  C-1 SL-1/SL-2 N-5 W-1 (C) 0.95 (80)(2) (60/40) (7) (3)  3 2 z51 C-2 SL-2/SL-4/SL-6 N-6 W-4 (C) 0.99 (100) (2) (40/59/1) (10)  (3)

The characters representing the ingredients in the above Tables standfor the following, respectively.

As to the acid generators, the characters used correspond to thosestanding for the compounds illustrated hereinbefore.

N-1: N,N-Dibutylaniline N-2: N,N-Dihexylaniline N-3:2,6-Diisopropylaniline N-4: Tri-n-octylamine N-5:N,N-Dihydroxyethylaniline N-6: 2,4,5-Triphenylimidazole W-1: MegafacF176 (produced by Dainippon Ink R Chemicals, Inc., a surfactant offluorine-containing type) W-2: Megafac R₀₈ (produced by Dainippon Ink &Chemicals, Inc., a surfactant of fluorine- and silicon-containing type)W-3: Organosiloxane polymer KP-341 (produced by Shin-Etsu Chemical Co.,Ltd., a surfactant of silicon-containing type) W-4: Troysol S-366(produced by Troy Chemical Industries, Inc.) W-5: PF656 (produced byOMNOVA Solutions Inc., a surfactant of fluorine-containing type) W-5:PF6320 (produced by OMNOVA Solutions Inc., a surfactant offluorine-containing type) SL-1: Cyclohexanone SL-2: Propylene glycolmonomethyl ether acetate SL-3: Ethyl lactate SL-4: Propylene glycolmonomethyl ether SL-5: γ-Butyrolactone SL-6: Propylene carbonate

The pattern forming methods (A) to (D) specified in the tables areexplained in the following Tables 5 and 6.

TABLE 5 Pattern forming method (A) An organic antireflective coatingARC29A (produced by Nissan Chemical Industries, Ltd.) is applied to asilicon wafer, and baked at 205° C. for 60 seconds, thereby forming anantireflective coating with a thickness of 78 nm. Thereon, a preparedpositive resist composition is coated, and baked at 120° C. for 60seconds, thereby forming a resist coating having a thickness of 250 nm.The thus obtained wafer is subjected to pattern exposure by means of anArF excimer laser immersion scanner (NA = 0.75) using purified water asan immersion liquid. Immediately after the exposure, water is fed ontothe wafer surface to form puddles, and then the wafer is dried by beingspun at 2,000 rpm to eliminate water. Next the wafer is heated at 120°C. for 60 seconds, and then developed with an aqueous solution oftetramethylammonium hydroxide (2.38 mass %) for 30 seconds, rinsed withpurified water, and further spin-dried. Thus, resist patterns areformed. (B) An organic antireflective coating ARC29A (produced by NissanChemical Industries, Ltd.) is applied to a silicon wafer, and baked at205° C. for 60 seconds, thereby forming an antireflective coating with athickness of 78 nm. Thereon, a prepared positive resist composition iscoated, and baked at 120° C. for 60 seconds, thereby forming a resistcoating having a thickness of 250 nm. The resist coating surface iscleaned by feeding purified water thereto and drying the water byspinning. The thus treated resist coating is subjected to patternexposure by means of an ArF excimer laser immersion scanner (NA = 0.75)using purified water as an immersion liquid. Immediately after theexposure, water is fed onto the wafer surface to form puddles, and thenthe wafer is dried by being spun at 2,000 rpm to eliminate water. Andthe wafer is heated at 120° C. for 60 seconds, and then developed withan aqueous solution of tetramethylammonium hydroxide (2.38 mass %) for30 seconds, rinsed with purified water, and further spin-dried. Thus,resist patterns are formed. (C) An organic antireflective coating ARC29A(produced by Nissan Chemical Industries, Ltd.) is applied to a siliconwafer, and baked at 205° C. for 60 seconds, thereby forming anantireflective coating with a thickness of 78 nm. Thereon, a preparedpositive resist composition is coated, and baked at 120° C. for 60seconds, thereby forming a resist coating having a thickness of 250 nm.The thus obtained wafer is subjected to pattern exposure by means of anArF excimer laser immersion scanner (NA = 0.75) using purified water asan immersion liquid. Thereafter, the wafer is heated at 120° C. for 60seconds, and then developed with an aqueous solution oftetramethylammonium hydroxide (2.38 mass %) for 30 seconds, rinsed withpurified water, and further spin-dried. Thus, resist patterns areformed.

TABLE 6 Pattern forming method (D) An organic antireflective coatingARC29A (produced by Nissan Chemical Industries, Ltd.) is applied to asilicon wafer, and baked at 205° C. for 60 seconds, thereby forming anantireflective coating with a thickness of 78 nm. On this coating, aprepared positive resist composition is coated, and baked at 120° C. for60 seconds, thereby forming a resist coating having a thickness of 250nm. Next, pattern exposure is performed by means of an ArF excimer laserimmersion scanner (NA = 0.75) using purified water as an immersionliquid. Immediately after the exposure, isopropyl alcohol is fed ontothe wafer surface for 15 seconds, and then the wafer is dried by beingspun at 2,000 rpm. Herein, the amount of isopropyl alcohol fed isadjusted to 0.5 kg/cm². And the wafer thus treated is heated at 120° C.for 60 seconds, and then developed with an aqueous solution oftetramethylammonium hydroxide (2.38 mass %) for 30 seconds, rinsed withpurified water, and further spin-dried. Thus, resist patterns areformed.

It is apparent from Tables 3 and 4 that development defect can beimproved by applying the present image forming methods.

Examples 21 to 25 and Comparative Example 4 (1) Formation of LowerResist Layer

On a 6-inch silicon wafer, FHi-028DD resist (an i-ray resist produced byFUJIFILM OLIN Co., Ltd.) was coated by means of a spin coater, Mark 8made by Tokyo Electron Limited, and baked at 90° C. for 90 seconds,thereby obtaining a uniform coating with a thickness of 0.55 μm.

This coating was further heated at 200° C. for 3 minutes to result information of a lower resist layer having a thickness of 0.40 μm.

(2) Formation of Upper Resist Layer

Solutions each having a solids concentration of 11 mass % were preparedby dissolving ingredients in solvents as shown in the following Table 7,and underwent microfiltration using a membrane filter having a porediameter of 0.1 μm, thereby preparing resist solutions for upper-layeruse. Each of the thus prepared resist solutions was coated on the lowerresist layer in the same manner as the lower resist layer was coated,and then heated at 130° C. for 90 seconds, thereby forming an upperresist layer having a thickness of 0.20 μm.

(3) Pattern Formation and Evaluation

Each of the upper resist layers was subjected to pattern exposure bymeans of an ArF excimer laser immersion scanner (NA=0.75) using purifiedwater as an immersion liquid. Immediately after the exposure, water wasfed onto the wafer surface and thereby puddles were formed. Thereafter,the wafer was dried by spinning at 2,000 rpm to eliminate the water.Next, the wafer was heated at 120° C. for 60 seconds, developed with anaqueous solution of tetramethylammonium hydroxide (2.38 mass %) for 30seconds, rinsed with purified water, and further dried by spinning.Thus, resist patterns were formed. Development defects of the thusformed resist patterns were evaluated by the same method as inExample 1. The evaluation results obtained are shown in Table 7.

Resins (SI-1) to (SI-5) in Table 7 are as follows:

(SI-1)

Molecularweight15000 (SI-2)

14500 (SI-3)

 9600 (SI-4)

Molecularweight 8900 (SI-5)

10800

TABLE 7 Composition Basic Number of Resin (A) Acid Generator Resin (C)Solvents Compound Surfactant Defects (2 g) (mg) (mg) (ratio by mass)(mg) (mg) (per cm²) Example 21 SI-1 z2 C-1 SL-2/SL-4 N-1 W-1 0.12 (80)(2) (70/30) (7) (5) 22 SI-2 z2/z51 C-2 SL-2/SL-4/SL-6 N-3 W-3 0.11(20/100) (2) (40/59/1) (6) (3) 23 SI-3  z65 C-1 SL-2/SL-4 N-5 W-1 0.10(100)  (2) (60/40) (7) (5) 24 SI-4 z2 C-3 SL-2/SL-4 N-3 W-6 0.15 (100)(3) (60/40) (10)  (5) 25 SI-5 z55 C-4 SL-2/SL-4 N-1 W-1 0.14 (80) (2)(70/30) (7) (5) Comparative Example  4 SI-1 z2 — SL-1/SL-2 N-5 W-1 2.13(80) (60/40) (7) (5)

As is clear from the results shown in Table 7, development defect can beimproved by use of the present pattern forming method.

Examples 26 to 34

Resists 1 to 6 were each prepared by dissolving ingredients in solventsas shown in the following Table 8 so as to prepare a solution having asolids concentration of 7 mass % and passing the solution through a0.1-μm polyethylene filter. Patterns were formed using each of the thusprepared resists in accordance with either of the methods as describedin Table 9, and evaluated by the same method as in Example 1. Resultsobtained are shown in Table 9.

TABLE 8 Composition Resin Acid Solvent Basic Resin (A) Generator (ratioCompound (c) Surfactant (2 g) (mg) By mass) (mg) (mg) (mg) Resist 1 21z25 SL-2 N-3/N-5 C-1 W-1 (80) (100) (3/3) (2) (3) Resist 2 22 z5/z55SL-2/SL-4 N-3/N-5 C-1 W-1 (50/50) (60/40) (3/3) (2) (3) Resist 3 23z5/z55 SL-1/SL-2 N-3 C-2 W-1 (50/50) (40/60) (6) (2) (3) Resist 4 24 z5SL-2/SL-4 N-5 C-2 W-1 (80) (60/40) (6) (5) (3) Resist 5 21 z2 SL-2/SL-4N-3/N-5 C-8 W-1 (100)  (70/30) (3/3) (1) (3) Resist 6 22 z2/z55SL-2/SL-4 N-3/N-5 C-8 W-1 (50/50) (70/30) (3/3) (5) (3)

TABLE 9 Pattern Number forming of defects Resist method (per cm²)Example 26 Resist 1 (D) 0.09 Example 27 Resist 2 (D) 0.11 Example 28Resist 3 (D) 0.08 Example 29 Resist 1 (B) 0.13 Example 30 Resist 2 (B)0.14 Example 31 Resist 3 (B) 0.11 Example 32 Resist 4 (D) 0.12 Example33 Resist 5 (B) 0.14 Example 34 Resist 6 (B) 0.13

It is apparent from these results that development defect can beimproved by the pattern forming methods of the invention.

According to the invention, it is possible to provide an immersionlithography-utilized image forming method which can ensure improveddevelopment defects.

The entire disclosure of each and every foreign patent application fromwhich the benefit of foreign priority has been claimed in the presentapplication is incorporated herein by reference, as if fully set forth.

1. A pattern forming method which uses a positive resist compositioncomprising: (A) a fluorine-free resin capable of increasing itssolubility in an alkaline developer under action of an acid; (B) acompound capable of generating an acid upon irradiation with an actinicray or radiation; (C) a fluorine-containing resin having at least onegroup selected from the group consisting of (X) an alkali-soluble group,(XI) a group capable of decomposing under action of an alkali developerand increasing solubility of the resin (C) in an alkaline developer and(XII) a group capable of decomposing under action of an acid andincreasing solubility of the resin (C) in an alkaline developer; and (D)a solvent, the method comprising: (i) a step of applying the positiveresist composition to a substrate to form a resist coating; (ii) a stepof exposing the resist coating to light via an immersion liquid; (iii) astep of removing the immersion liquid remaining on the resist coating;(iv) a step of heating the resist coating; and (v) a step of developingthe resist coating.
 2. The pattern forming method according to claim 1,wherein the resin (A) has a mononuclear or polynuclear alicyclichydrocarbon structure.
 3. The pattern forming method according to claim1, wherein the resist coating is exposed to light of a wavelength of 193nm.
 4. The pattern forming method according to claim 1, furthercomprising a step of cleaning the resist coating surface prior to (ii)the step of exposing the resist coating to light via an immersionliquid.
 5. The pattern forming method according to claim 1, wherein(iii) the step of removing the immersion liquid remaining on the resistcoating is a step of removing the immersion liquid by feeding awater-miscible organic solvent onto the resist coating.
 6. The patternforming method according to claim 5, wherein the water-miscible organicsolvent is isopropyl alcohol.
 7. The pattern forming method according toclaim 1, wherein the resin (C) has a weight average molecular weight of1,000 to 100,000.
 8. The pattern forming method according to claim 1,wherein the resin (C) is added in an amount of 0.1 to 5 mass % based onthe total solids in the positive resist composition.
 9. The patternforming method according to claim 1, wherein (iii) the step of removingthe immersion liquid remaining on the resist coating comprises forming aliquid film (puddle) of the immersion liquid and then removing theliquid film so as not to left any liquid drops.
 10. The pattern formingmethod according to claim 9, wherein the step of removing the liquidfilm is a step of removing the liquid film while rotating the substrateat 500 rpm or above.
 11. The pattern forming method according to claim1, wherein the resin (A) comprises a repeating unit having a polycyclichydrocarbon group substituted by a hydroxyl group or a cyano group. 12.The pattern forming method according to claim 1, wherein the resin (C)is an alkali-soluble resin having the alkali-soluble group (X), and thealkali-soluble group (X) is represented by —C(CF₃)(CF₃)(OH).
 13. Thepattern forming method according to claim 1, wherein the resin (A)comprises: a repeating unit represented by formula (A1); a repeatingunit represented by formula (A2); and a repeating unit represented byformula (A3),

wherein Xa, Xb and Xc each independently represents a hydrogen atom or amethyl group, R₁ represents a univalent organic group having a lactonestructure, R₂ represents a univalent organic group having a hydroxylgroup or a cyano group, and R₃ represents a univalent organic groupcapable of splitting off by the action of an acid.